Rh/Ni wet-impregnated: Ia 3 d mesostructured aluminosilicate and r-GO catalysts for hydrodeoxygenation of phenoxybenzene

Article abstract of DOI:10.1039/c7nj00367f

Rh/Ni bimetallic supported bifunctional 3D porous aluminosilicate and Rh/Ni supported reduced graphene oxide (r-GO) catalysts were synthesised and their structural properties evaluated by XRD, BET-surface area, FT-IR, NH₃-TPD, H₂-TPR, ICP-OES, HRTEM-EDAX and XPS analysis. The catalytic activities of the Rh/Ni/Al-KIT-6 and Rh/Ni-rGO catalysts were investigated by analysis of the vapour phase hydrodeoxygenation (HDO) of diphenyl ether and guaiacol. The Rh/Ni/Al-KIT-6 catalyst exhibited the best catalytic performance for vapour phase HDO of diphenyl ether at 420 °C with a WHSV of 3.6 h^-1. In addition, lignin derived guaiacol was also investigated and the desired product of benzene was not achieved for both the Rh/Ni/Al-KIT-6 and Rh/Ni/r-GO catalysts. The Rh/Ni/Al-KIT-6 catalyst demonstrated excellent stability, due to the acidic Al-KIT-6 support which stabilizes the Rh/Ni particles on the surface. However, a higher dispersion of Rh/Ni species was observed on the Rh/Ni/Al-KIT-6 catalyst, as evidenced by HR-TEM imaging, which is mainly due to the large surface area of the Al-KIT-6 support, while the Rh/Ni/r-GO catalyst exhibited larger metal aggregates due to weak Rh/Ni interactions with the reduced graphene oxide (r-GO) support, resulting in a smaller surface area for this catalyst which could restrict the distribution of Rh/Ni particles. Superior catalytic activity towards the C-O bond cleavage of diphenyl ether and guaiacol was observed for the Rh/Ni/Al-KIT-6 catalyst. The superior catalytic activity of this catalyst is mainly due to the highly dispersed small Rh/Ni bimetallic species and their interactions with the mesoporous cubic acidic support via the hydrogen spill over effect, which favours the earlier NiO reduction, and which was confirmed by H₂-TPR and HR-TEM. The Rh/Ni/Al-KIT-6 catalyst exhibit excellent catalytic properties, with 60% benzene selectivity observed. Furthermore, the bifunctional behaviour of the Rh/Ni/Al-KIT-6 catalyst, with its unique cubic morphology support in addition to the uniform dispersion of Rh/Ni species, could enhance diphenyl ether conversion and benzene selectivity.

Full text of DOI:10.1039/c7nj00367f

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The role of atropisomers on the photo-reactivity and fatigue of
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Page 1 of 32
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Rh/Ni wet-impregnated Ia3d mesostructured aluminosilicate and r-GO catalyst for
hydrodeoxygenation of phenoxy benzene
*
Pichaikaran Sudhakar, Arumugam Pandurangan
Department of Chemistry, Anna University, Chennai 600 025, India
*
Corresponding author at: Tel.: +91 44 22358653; fax: +91 44 22200660.
Eꢀmail address: pandurangan_a@yahoo.com (A. Pandurangan)
Graphical abstract:
1

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Abstract
Rh/Ni bimetal supported bifunctional 3D porous aluminosilicate and Rh/Ni supported
reduced graphene oxide (rꢀGO) catalyst was synthesised and evaluated their structural
3 2
behaviour by XRD, BETꢀSurface area, FTꢀIR, NH ꢀTPD, H ꢀTPR, ICPꢀOES, HRTEMꢀ
EDAX and XPS analysis. The catalytic activity of Rh/Ni/AlꢀKITꢀ6 and Rh/NiꢀrGO catalyst
was investigated by vapour phase hydrodeoxygenation of diphenyl ether and guaiacol. The
Rh/Ni/AlꢀKITꢀ6 catalyst exhibited best catalytic performance on vapour phase HDO of
o
ꢀ1
diphenyl ether at 420 C with WHSV 3.6 h . In addition, another lignin derived guaiacol was
also probed and the desired product of benzene from guaiacol was not achieved on Rh/Ni/Alꢀ
KITꢀ6 and Rh/Ni/rꢀGO catalyst. Besides, Rh/Ni/AlꢀKITꢀ6 catalyst showed excellent stability
due to the acidic AlꢀKITꢀ6 support, which stabilizes the Rh/Ni particles on the surface.
However, the higher dispersion of Rh/Ni specious maximum observed on Rh/Ni/AlꢀKITꢀ6
catalyst as evidenced by HRꢀTEM image and it mainly due to their large surface area of Alꢀ
KITꢀ6 support, while Rh/Ni/rꢀGO catalyst shows larger metal aggregates due to weak Rh/Ni
interaction with reduced graphene oxide (rꢀGO) support and furthers a narrow surface area in
this catalyst could restricted the higher distribution of Rh/Ni particles. The superior catalytic
activity in the CꢀO bond cleavage of diphenyl ether and guaiacol has been observed in
Rh/Ni/AlꢀKITꢀ6 catalyst. The superior catalytic activity of this catalyst mainly due to the
highly dispersed small Rh/Ni bimetallic species and further Rh/Ni interaction with
mesoporous cubic acidic support via hydrogen spill over effect, which was favour the earlier
2
NiO reduction, and it was confirmed by H ꢀTPR and HRꢀTEM. The Rh/Ni/AlꢀKITꢀ6 catalyst
displayed excellent catalytic properties with 60 % benzene selectivity. Further, the
bifunctional behaviour in this Rh/Ni/AlꢀKITꢀ6 catalyst with unique cubic morphology
support, in addition to uniform dispersion of Rh/Ni species could enhance the diphenyl ether
conversion and benzene selectivity.
Keywords: Diphenyl ether, guaiacol, benzene, AlꢀKITꢀ6, rꢀGO, Rh/Ni bimetal
2

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Introduction
The modern civilization was highly suffered against decay of petroleum reservoir due to
their limited resources and another horrible crisis is CO emission. Since, the potential usage
of alternative sources such as lignocellulosic biomass is find an great opening for replacing
fossil fuel and regulating CO emission. Moreover, the lignin feedstock from lignocellulosic
2
2
biomass containing aryl ethers and phenolic compounds are significant for producing
1
gasoline range hydrocarbon through CꢀO bond cleavage . Lignin is a three dimensional
9
network bioꢀpolymer containing C ꢀpropyl unit attached with CꢀC, and CꢀO chains and it
treated with mild condition to produce phenolic monomers and dimers such as phenol, alkylꢀ
’
guaiacols, alkylꢀsyringols and dimers like βꢀOꢀ4, 4ꢀOꢀ5 ether linkage and 5–5 , βꢀ1 C–C
2
linkage . The 4ꢀOꢀ5 linkage is the strongest linkage in the lignin molecule and diphenyl ether
is considered as model 4ꢀOꢀ5 linkage compound and further the diphenyl ether CꢀO bond
3
cleavage need severe conditions . However, the current utilization of liquid transportation
fuel from lignin monomer and dimer is critical due to their higher oxygen ratio and this
1
,4
circumstances will decreases the fuel quality . Furthermore, for understanding the
conversion process of real bioꢀoil into liquid fuel or chemical is still difficult due to the
presence of complex mixtures with higher oxygen functionalities in the bioꢀoil. Hence, more
attention has been paid on study of individual lignin model compound for understanding
5
reaction chemistry before upgrading of real lignin bioꢀoil . In these aspects, the less reactive
phenolic compound like guaiacol and diphenyl ether have significantly attracted for studying
2
,6
HDO model reaction . Hence, hydrodeoxygenation is an efficient process for oxygen
removal and further upgrading of better quality of fuel from their lignin monomer. The high
degree of hydrodeoxygenation catalyst with minimum hydrogen consumption is still a major
challenge in the area of catalysis. As reported earlier, the high selectivity and conversion of
7
,8
ligninꢀderived phenolic monomer and dimer was catalysed by transition metal , transition
9
1,10,11
metal sulphide , and transition metal phosphides catalysts
. However, these catalysts
were severely affected by deactivation and drastic experimental conditions; additionally, the
sulphur contamination in sulphided catalyst also created a serious disadvantage. In these
aspects, the advantages of mesoporous metal oxide supported bimetallic catalysts has
significantly attracted because of its high structure regularity, controlling the metal oxide
particle size, limiting the growth of metal cluster size and offered better dispersion over the
12–14
external surface
.
3

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Also, the type of support has significantly enhanced the rate of chemical reaction in the
mono and bimetal supported catalysts. The various catalytic supports such as clay, zeolite,
mixed oxides, carbon materials and mesoporous materials have been developed and tested by
1
5,16
others with substantial progress
. Although the use of these support was paid less attention
due to their limited surface area for available active sites, limited pore size and restricted
hydrothermal stability. Consequently, the dilemma was conquer by using the invention of
new class of mesoporous Ia3d cubic silica (KITꢀ6) support possessing higher surface area,
large meso and micropores, thicker pore walls, higher hydrothermal stability, tunable 3D
interconnected mesopores, which allows better dispersion of active species with faster
12,15
diffusion of reactants and products, reproducibility, etc.,
In this contribution with the aim of increasing the HDO activity, we choosing Rh/Ni
supported mesoporous aluminosilicate bimetallic catalysts. The catalyst was synthesised by
wetꢀimpregnation method and further their catalytic activity was investigated over vapour
phase CꢀO bond cleavage of diphenyl ether and guaiacol under different experimental
condition. Moreover, the activity pattern of mesoporous catalyst was compared with reduced
graphene oxide supported Rh/Ni bimetal catalyst under the specific reaction condition.
Further, the reaction pathway of diphenyl ether and guaiacol were investigated with respect to
Rh/Ni bimetal catalyst. However, the catalytic reaction so far carried out using diphenyl ether
17ꢀ25
and bimetallic system by the authors in the literature, using higher hydrogen pressure
.
Therefore, in the present work was carried out under atmospheric hydrogen pressure and it
showed highest diphenyl ether conversion. Further, Rh/Ni/AlꢀKITꢀ6 has been characterized
by different physicochemical techniques for found the relationship between the catalytic
properties and their HDO activity of diphenyl ether. Eventually, the deactivation and
regeneration behaviour of bimetallic catalyst was studied briefly and further evaluated their
regeneration activity with respect to diphenyl ether conversion. Therefore, their study could
afford significant information about Rh/Ni bimetal system for improving the upgrading
process of lignin bio oil via diphenyl ether model substrate, under the present atmospheric
pressure condition.
4

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Experimental
Materials
Pluronic P123 [Poly (ethylene glycol)ꢀblockꢀpoly (propylene glycol)ꢀblockꢀpoly
ethylene glycol), (EO20 Aldrich: M.W.5800, >98%pure)],
(
PO70
EO20;
tetraethylorthosilicate (TEOS; Aldrich, >98% pure), nꢀButanol (SRL Biochem, 99.5 % pure),
hydrochloric acid (HCL; SRL Biochem, 35 %), deionised water (Evergreen India Ltd),
aluminiumisopropoxide (AlfaꢀAesar) were used for the synthesis of AlꢀKITꢀ6 support.
Graphite powder (99 % pure, SigmaꢀAldrich), concentrated sulphuric acid (H SO ; SRL, 98
2
4
%
), potassium permanganate (KMnO
hydrazine hydrate (99 % pure, Fischer Scientific) were used for synthesis of graphene oxide
GO) and reduced graphene oxide (rꢀGO). Rhodium (III) chloride (AlfaꢀAesar), nickel (II)
4 3
; SRL, 99.5 %), sodium nitrate (NaNO ; SRL, 99.5 %),
(
nitrate hexahydrate (Aldrich) was used for preparation of metal supported catalyst. Diphenyl
ether (SRL Biochem, 98 % pure) and Guaiacol (SRL Biochem, 99 % pure) were used in
catalytic reaction. The entire chemicals used in the synthesis and reactions are AR grade and
used without any further purification.
Preparation of Catalysts
AlꢀKITꢀ6 support was synthesised using triblockcopolymer surfactant as a structure
directing agent and used with mild acidic conditions. A classic procedure for the synthesis of
2
6
AlꢀKITꢀ6 (25) support with Si/Al ratio 25 was follows by reported in the literature . 4 g of
Pluronic P123 was added to 144 mL of deionised water in a polypropylene bottle with 7.9 g
of 35 % HCL and stirred for 4 h under atmospheric condition. Followed by stirring for 4 h, an
apparent homogeneous solution was formed then 4 g of nꢀbutanol was added and further
stirring was continued for 1 h. Then, 8.4 g of TEOS added slowly and followed by calculated
weight of aluminiumisopropoxide was added. The obtained mixture was stirred for 24 h at 35
o
o
C and hence the mixture was hydrothermally treated under closed condition at 100 C for 24
h. After hydrothermal treatment, the obtained solid material was filtered hot without washing
o
and further dried the material at 100 C for 12 h. Finally the material was crushed and grained
o
by mortar and the obtained fine powder was calcined at 540 C in air atmosphere for 24 h to
expel the surfactant. The recovered final material was denoted as AlꢀKITꢀ6 (25) support.
Graphene oxide (GO) was synthesised using graphite powder by the modified
2
7–31
Hummer’s method
. The complete synthesis procedures are as follows: 3 g graphite
5

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powder and 1.5 g sodium nitrate were mixed properly in a 1000 mL round bottom flask then
69 mL of con.sulphuric acid was added in iceꢀbath with continuous stirring. After 20 min, 9 g
o
of KMnO
4
was added slowly to the above mixture under the temperature below 20 C to
o
avoided explosion. The mixture was stirred at 35 C in an oilꢀbath for 2 h after it was diluted
by adding 138 mL of deionised water and further stirring continued for 12 h. Then, the
o
reaction mixture was heated to 80 C for 1 h and reaction temperature was maintained to
ambient condition. Further, the oxidation of graphite with KMnO
4
was completed by the
treatment of 30 % H solution (10 mL) and then diluted with 400 mL of deionised water.
2
O
2
The pH of the suspension was around 1 and kept for 12 h to separate the water and GO.
Furthermore, the suspension was repeatedly washed with 10 % aq.HCl and deionised water
until neutral pH was attained. Finally, the graphene oxide was filtered and dried overnight at
o
5
0 C.
32,33
The obtained graphene oxide (GO) was reduced by chemical method
. Typically, 1
g of graphene oxide (GO) added with 10 mL of deionised water and ultrasonicated for 1 h,
o
then 10 mL of hydrazine hydrate was added. Further, the mixture was heated at 100 C in a
refluxed condenser for 2 h. After reflux, the reduced graphene oxide was precipitated, filtered
o
and washed thoroughly with deionised water and finally dried at 50 C. The obtained black
coloured solid material was rꢀGO and used as support for preparing bimetal catalyst.
Rhodium and nickel supported mesoporous AlꢀKITꢀ6 and reduced graphene oxide (rꢀ
34–36
GO) bimetallic catalysts were prepared by wetꢀimpregnation method
. About 1g of each
support separately transferred into a 50 mL round bottom flask and added 30 mL of deionised
water and stirred for 15 minutes. The precursor salt of rhodium (1.0 Wt %) and nickel (7.0
Wt %) were added and stirring was continued for 6 h. After stirring the water from the
o
mixture was evaporated at 100 C for 12 h. Finally the material was crushed and grained by
o
mortar. The obtained fine powder was calcined at 450 C for 6 h under atmospheric air. The
obtained solid material was individually represented as 1.0 % Rh/7.0 % Ni/AlꢀKITꢀ6 & 1.0 %
Rh/7.0 % NiꢀrGO .
Materials characterization
The crystallographic features of bimetallic catalysts were investigated by powder XRD
analysis, which was obtained from Bruker D8 Advanced Xꢀray diffractometer with a CuKα
radiation source. The specific surface area, pore volume and pore size distribution of
bimetallic catalysts were performed by nitrogen adsorption techniques at liquid nitrogen
o
temperature (ꢀ195.657 C). N physisorption analysis were performed on micromeritics asap
2
6

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o
2
020 porosimeter, Prior to nitrogen physisorption the sample was outgassed at 200 C for 12
h. The specific surface area was measured by BET method and the pore volume, pore size
distribution were measured by BJH method. Attenuated total reflectionꢀinfrared (ATRꢀIR)
Perkin ElmerꢀSpectrumꢀtwo spectrophotometer was used for finger region of support and
catalysts. The shape and metal oxide crystallite size of bimetallic catalysts were obtained
from HRꢀTEM images using JEOL 3010 instrument with a UHR polepiece which gives
lattice resolution around 0.14 nm, before analysing HRꢀTEM, the sample was well dispersed
in acetone using sonication for 30 min. The dispersed sample was placed in a copper grid and
the volatile solvent was evaporated before sample was evaluated for HRꢀTEM imaging. The
elemental compositions present in the catalysts were performed with a Perkins–Elmer Optima
5300Dv inductively coupled plasma optical emission spectrometry (ICPꢀOES). The
reduction behaviour of metal oxide was performed in Chemisorb 2750 TPD/TPR
micrometrics equipment with a thermal conductivity detector (TCD). The sample was preꢀ
o
treated at 500 C under air flow for 1 h to clean the surface of the catalyst. After cleaning the
surface of the catalyst about 100 mg of the solid sample was treated with helium gas (25 mL
ꢀ1
o
ꢀ1
min ) for 1 h at 115 C, after that the reducing gas mixture (5 vol. % H /Ar, 25 mL min )
2
was transferred into the sample port at room temperature until the base line was obtained and
o
o
ꢀ1
further the temperature was increased to 1000 C at a heating rate of 10 C min . The acidic
properties of AlꢀKITꢀ6 support and bimetallic catalyst was investigated by temperature
programmed desorption of ammonia (NH
3 3
ꢀTPD). The NH ꢀTPD experiment were carried out
in a similar Chemisorb 2750 TPD/TPR flow reactor, initially the sample was preꢀtreated at
o
o
5
00 C for 1 h with helium flow and further ammonia was introduced at 50 C for removing
the physically adsorbed ammonia with purging of helium flow until the base line was started.
o
o
ꢀ1
Further, ammonia desorption started up to 600 C with a heating rate of 10 C min .
Catalytic experiment
All the catalytic reactions were carried out in a vapour phase fixed bed reactor under
atmospheric pressure conditions. The reaction parameter viz, temperature, weight hourly
space velocity WHSV, and timeꢀonꢀstream was studied. Hydrodeoxygenation of diphenyl
ether and guaiacol were studied as biomass representative compound. Before starting the
o
catalytic reaction, the bimetallic catalyst was activated at 500 C under hydrogen flow rate of
ꢀ1
5
0 mL min then the reactor was cooled to room temperature. Further, the reaction was
o
o
carried out at 370 C and 420 C with three different WHSV and at timeꢀonꢀstream of 15 h.
7

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During the catalytic run, the reaction products were sampled at every one hour intervals and
further the sample was analysed using offꢀline gas chromatography equipped with flame
ionisation detector (FID) and an Rtxꢀ5 column. The conversion of diphenyl ether or guaiacol
(X) was defined as the percentage of diphenyl ether or guaiacol converted to all the different
products. The selectivity to benzene (S) is defined as the amount of benzene obtained was
dived by the amount of diphenyl ether or guaiacol converted to all the products.
Results and Discussion
Physicochemical properties of catalysts
Powder X-ray Diffraction (XRD)
Figure 1(A) Low angle XRD patterns of AlꢀKITꢀ6 support and Rh/Ni/AlꢀKITꢀ6 catalyst
Figure 1(A) represented smallꢀangle XRD pattern of mesoporous AlꢀKITꢀ6 support
and the bimetal impregnated material. The diffraction signals of support shows at 2θ= 0.9,
corresponds to (211) reflection and a very tiny hump observed at 2θ= 1.2 corresponds to
(
220) reflection. The main reflection pattern of (211) plane with unit cell parameter a
nm was calculated from the expression a
= √6 × d(211), which was confirmed that the support
possessing bicontinuous ordered mesostructured with Ia3d cubic space group symmetry .
The unit cell parameter a for AlꢀKITꢀ6 support and Rh/Ni/AlꢀKITꢀ6 catalyst was represented
in Table 1. The a value for AlꢀKITꢀ6 support showed 20.9 nm, while Rh/Ni/AlꢀKITꢀ6
o
= 20.9
o
2
6
o
o
showed 20.4 nm. However, the a
o
value of Rh/Ni/AlꢀKITꢀ6 was slightly less than the AlꢀKITꢀ
6
support and it represented the presence of small metal oxide particles occupied on the
8

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pores. Further a small peak shifted towards higher angle and diminished peak intensity was
observed in Rh/Ni/AlꢀKITꢀ6 with respect to AlꢀKITꢀ6 support and this behaviour was not
alter the textural properties of Rh/Ni/AlꢀKITꢀ6 bimetallic catalyst as evidenced by the HRꢀ
2
TEM and N ꢀsorption analysis.
Figure 1(B) represented high angle XRD pattern of Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO
o
o
o
o
catalysts. The diffraction peak exhibited at 2θ angle of 37.1 , 43.1 , 62.7 , and 75.5 designate
3
7
cubic NiO of Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO catalysts . However, the diffraction signal of
Rh
2
O
3
phase was not identified in both catalysts because of the fine dispersion of these nanoꢀ
o
particles on the support. Though, a small hump was observed at 2θ angle of 41 in the
Rh/Ni/AlꢀKITꢀ6 catalyst indicated metallic rhodium.
Figure 1 (B) High angle XRD patterns of calcined Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO catalysts
9

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Table 1 Textural Properties, surface acidity and coke content of Rh/Ni/AlꢀKITꢀ6 and
Rh/Ni/rꢀGO catalysts
Metal
content
b
c
d
e
f
Total
acidity
[mmol/g]
a
a
o
S
BET
V
total
P
D
P
W
g
h
Sample
2
3
Coke [wt %]
[
nm] [m /g] [cm /g] [nm] [nm]
[%]
Diphenyl
ether
Rh
-
Ni
-
Guaiacol
56*
Al-KIT-6(25)
20.9
684
582
124
1.10
0.90
0.32
6.8
6.4
3.6
3.8
-
0.34
0.31
-
-
Rh/Ni /Al-KIT-6 0.95 6.75
20.4
5.1
4.4
8.5
9.3
Rh/Ni /r-GO
0.93 6.67
-
18.1
*
a
b
c
value obtained by ICPOES techniques
Metal concentration obtained by ICPOES techniques
Values calculated from low angle XRD
Surface area obtained from BETꢀSurface area analysis
Total pore volume obtained from adsorption isotherm
Pore size distribution acquired by BJH method
d
e
f
w o
Wall thickness of AlꢀKITꢀ6 and Rh/Ni/AlꢀKITꢀ6 calculated from the expression P = a /2ꢀ
P
D
o
where a = √6 × d(211)
g
Total acidity obtained by NH
3
ꢀTPD technique
h
Coke content of spent catalyst determined by TGAꢀtechnique
1
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2
N Physisorption
Figure 2 (A & B) Nitrogenꢀadsorption desorption isotherms for AlꢀKITꢀ6 support and
Rh/Ni/AlꢀKITꢀ6, Rh/Ni/rꢀGO catalyst with inset BJH pore size distribution
Figure 2(A & B) represents nitrogen adsorptionꢀdesorption isotherms of support and
Rh/Ni supported bimetallic catalysts with inset BJH pore size distribution. The AlꢀKITꢀ6
support and Rh/Ni/AlꢀKITꢀ6 showed narrow pore size distribution with average pore size
distribution of AlꢀKITꢀ6 showed 6.8 nm. Ia3d cubic mesoporous AlꢀKITꢀ6 support and Rh/Ni
1
supported catalysts shows type IV isotherms with H hysteresis loop obtained at higher
relative pressure indicating large pore size in a narrow type. The initial nitrogen adsorption in
lower relative pressure at 0.5 for AlꢀKITꢀ6 attributed monolayer adsorption of micropores
and mesoporous, whereas the Rh/Ni/AlꢀKITꢀ6 catalyst extend the relative pressure P/Po at
15
higher order in the range of 0.6ꢀ0.8 attributing capillary condensation inside the mesopores .
The surface area, pore volume and pore diameter for AlꢀKITꢀ15 support and Rh/Ni/AlꢀKITꢀ6
catalyst was shown in Table 1. Generally the surface area, pore volume and pore diameter
decreases as in the case of Rh/Ni/AlꢀKITꢀ6 catalysts than the AlꢀKITꢀ6 support, this may be
due to the presence of Rh/Ni oxide particles occupied over the surface as well as pores.
Figure 2 (B) and inset shows the nitrogen sorption isotherm and pore size distribution of
Rh/Ni supported rꢀGO catalyst, according to the IUPAC classification the catalyst shows
3
9
2
ꢀ1
3
type IV isotherm with H hysteresis loop and specific surface area was found 124 m g .
The surface area, pore volume and pore diameter were presented in Table 1. On comparing
the textural properties of Rh/Ni/KITꢀ6 and Rh/Ni/rꢀGO catalysts, the mesoporous catalyst
seems to have superior textural characteristics than reduced graphene oxide supported
catalyst.
1
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FT-IR Spectroscopy
Figure 3 FTꢀIR spectra of support and Rh/Ni supported bimetallic catalysts
Figure 3 represented FTꢀIR spectra of support and metal oxide supported bimetallic
ꢀ1
ꢀ1
ꢀ1
catalysts. AlꢀKITꢀ6 support shows framework band at 463 cm , 811 cm , 961 cm , 1100
ꢀ1
ꢀ1
39
cm and the shoulder peak at 1210 cm corresponds to mesoporous AlꢀKITꢀ6 support .The
ꢀ1
band at 1100 and the shoulder band at 1210 cm represented assymetric stretching mode of
ꢀ1
siloxane (SiꢀOꢀSi) while the band at 811 cm corresponded to symmetric stretching mode of
ꢀ1
SiꢀOꢀSi linkage of framework AlꢀKITꢀ6. Further, the band at 463 cm confirmed SiꢀOꢀSi and
39–41
SiꢀOꢀAl bending vibration in the mesoporous framework
. Additionally, the band at 970
ꢀ1
cm attributed silanol group (SiꢀOH) in the mesoporous solid or a stretching mode of SiO
4
3
9
unit bonded to Al atom . The FTꢀIR spectrum of Rh/Ni/AlꢀKITꢀ6 mesoporous bimetallic
catalysts showed absorption band similar to AlꢀKITꢀ6 support which indicated structural
4
2
stability of AlꢀKITꢀ6 support . Moreover, the intensity of the transmittance band sharply
increased below the framework region as compared with AlꢀKITꢀ6 support after Rh/Ni
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2

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43,44
deposition . FTꢀIR spectrum of graphene oxide shows the vibration mode of CꢀOꢀC
ꢀ1
2
ꢀ1
epoxide linkage at 1230 cm and the sp hybridized C=C plane vibration shows at 1630 cm .
ꢀ1
However, the keto group C=O appeared at 1850 cm and the OH stretching vibration due to
ꢀ1
ꢀ1
water molecule appeared at 3380 cm and CꢀOH, CꢀO vibration appeared at 1386, 1051 cm
46–49
respectively, which confirmed the formation of graphene oxide
. The FTꢀIR spectrum of
reduced graphene oxide (rꢀGO) was shown in Figure 3 which on compared to graphene oxide
(GO) was entirely different. This confirmed the reduction of various CꢀOH and CꢀO bond
2
from the keto and carboxylic acid groups and further sp hybridised C=C vibration appeared
ꢀ1 47,48
at 1640 cm
. The FTꢀIR spectrum of Rh/Ni/rꢀGO catalyst was represented in Figure 3,
ꢀ1
here the sharp C=C band at 1640 cm similar to rꢀGO support confirmed the absence of any
structural deformation in the catalyst.
3
Temperature programme desorption of ammonia (TPD-NH )
Figure 4 AmmoniaꢀTPD spectra of AlꢀKITꢀ6 support and Rh/Ni/AlꢀKITꢀ6 catalyst
1
3

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The surface acidic characteristics of mesoporous AlꢀKITꢀ6 support and Rh/Ni/Alꢀ
KITꢀ6 bimetallic catalyst were probed through NH ꢀTPD analysis. Acid sites are classified
based on the strength of desorbed ammonia with respect to temperature, usually weak (<200
3
o
o
o
o
49
C), medium (200 Cꢀ350 C) and strong acid sites (>350 C) . Figure 4 represents ammonia
desorption peaks of AlꢀKITꢀ6 support and Rh/Ni/AlꢀKITꢀ6 bimetallic catalyst. The broad
peak with the area under the maximum ammonia desorption in AlꢀKITꢀ6 support implies that
the support mostly gave medium and strong acid sites. However, Rh/Ni/AlꢀKITꢀ6 bimetallic
catalyst shows weak, medium, and strong acid sites and the measured total acidity of the
support and catalyst was represented in Table 1. The area under the TPD curve for Rh/Ni/Alꢀ
KITꢀ6 shows mainly weak and medium acid sites. Further, the hydrogenolysis of diphenyl
ether and guaiacol required medium acid sites for cleavage of CꢀO bond and it was confirmed
by the higher conversion of diphenyl ether and guaiacol obtained on Rh/Ni/AlꢀKIT6
bimetallic catalyst than nonꢀacidic Rh/Ni/rꢀGO bimetallic catalyst. However, the total acid
sites in bimetallic catalyst was relatively lower than the support, this may be due to the acid
sites being occupied by the metallic sites.
2
Temperature programme reduction of hydrogen (TPR-H )
2
Figure 5 H ꢀTPR spectra of Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO catalysts
1
4

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The temperature programmed reduction of rhodium and nickel supported bimetallic
catalysts were depicted in Figure 5. As reported from the previous work the mono metallic
o
o
nickel supported catalysts showed the reduction maxima of NiO at 375 C and 524 C, which
50
implied the hard reduction of nickel oxide particles . However, the individual reduction
5
1
2 3
peak of Rh O was not observed on bimetallic catalyst . Besides, the Rh/Ni/AlꢀKITꢀ6
o
o
o
bimetallic catalysts showed three reduction maxima at 288 C, 575 C, and 785 C, which
indicated simultaneous reduction of both Rh and Ni particles and the reduction maxima of
5
1
NiO shifted to lower temperature via hydrogen spillover effect . Though, the lower reduction
o
shift of NiO was considerably observed at 288 C and the maximum hydrogen consumption
o
was observed at 575 C attributing higher surface nickelꢀrhodium atoms and furthers a sharp
o
reduction peak at 785 C indicating small amount of large metal oxide crystallites strongly
interact with acidic support. The reduction properties of rhodiumꢀnickel oxidic species
o
o
observed in the case of Rh/Ni/rꢀGO catalyst at 257 C and 615 C. The reduction peak at 615
o
C indicate maximum reduction point of RhꢀNi species, and the broader peak in the range
o
o
between 411 Cꢀ711 C specified variable reduction size of RhꢀNi species. While, the peak at
o
2
57 C illustrated well dispersed RhꢀNi species, on comparing the reduction behaviour of Alꢀ
KITꢀ6 and rꢀGO supported Rh/Ni bimetallic catalysts, AlꢀKITꢀ6 acidic support significantly
improved the reduction properties of Rh/Ni bimetallic species towards lower reduction sites.
HR-TEM analysis
The HRꢀTEM images with statistical analysis of Rh/Ni/Al/KITꢀ6 and Rh/Ni/rꢀGO
was represented in Figure 6 (A). Figure 6 (A) for Rh/Ni/AlꢀKITꢀ6 bimetallic catalyst showed
metal particles with meso structure and indeed, no particles larger than 24 nm could be
viewed as confirmed by the statistical analysis. Furthermore, the particle was highly
distributed in the range over 6ꢀ14 nm and most of the particles located on the surface of the
catalyst and further the existence of Rh/Ni species on the catalyst confirmed with EDAX
analysis which was represented in Figure 6 (B). Moreover, Figure 6(A) showed HRꢀTEM
images with statics analysis of Rh/Ni/rꢀGO catalyst and corresponding EDAX spectrum was
represented in Figure 6 (B). Here the appearance of bimetallic species was entirely different
with mesoporous supported catalyst, and in these catalysts the metal particles was slightly
aggregated from the support surface. It may be due to the weak interaction between the metal
and carbon support. Though, the particle size estimated by statics analysis was not exceeds 16
nm and all the particles was present on the external surface of the catalyst.
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5

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Figure 6 (A) HRꢀTEM images with statics analysis of Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO
bimetallic catalyst
Figure 6 (B) EDAX analysis of Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO bimetallic catalyst
1
6

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XPS analysis
Figure 7 (A & B) XPS analysis of Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO bimetallic catalyst: (A)
Rh3d, (B) Ni2p
The oxidation state of Rh/Ni bimetallic catalysts were investigated by XPS analysis.
The XPS spectrum of rhodium oxide in Rh/Ni/Al/KITꢀ6 and Rh/Ni/rꢀGO were presented in
Figure 7 (A). The presence of Rh 3d5/2 spins state corresponding to the binding energy 309.9
5
3
2ꢀ54 .
eV on both catalysts confirmed Rh exist in +3 oxidation state in the form of Rh O
.
2
However, the position of metallic Rh at binding energy 307.2 eV was not observed in
reduced graphene oxide supported catalyst, whereas in the silica supported Rh/Ni catalyst
shows very trace amount of metallic Rh in the region of 307.1 eV, this factor may be
enhanced the additional diphenyl ether conversion. The XPS spectrum of nickel oxides on
both Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO catalysts were shown in Figure 7 (B). Here, Rh/Ni/Alꢀ
KITꢀ6 shows two spin states Ni2p3/2 and Ni2p1/2 with binding energy 855.5eV and 871.1eV
5
5
respectively . However, Rh/Ni/rꢀGO catalyst shows Ni2p3/2 signal at 854.4 eV and Ni2p1/2
5
6ꢀ59
signal at 873.2 eV respectively
, the binding energy value 854.4 eV with respect to Ni2p3/2
2
+
signal illustrated pure Ni in Rh/Ni/rꢀGO catalyst in the form of NiO. With respect to this
pure NiO, additional NiO phase shift highly observed in Rh/Ni/rꢀGO catalyst towards higher
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7

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binding energy around 2.1 eV. Mostly, the NiO reduction was simple towards lower binding
5
5,58
energy region
catalyst shows this shift around 1.1 eV, this lower shift may enhance the reduction of NiO by
the addition of Rh in the silica support than in the carbon support.
. In these aspects on compared with Rh/Ni/rꢀGO catalyst, Rh/Ni/AlꢀKITꢀ6
2
O
3
3.2 Catalytic process of diphenyl ether and guaiacol
The catalytic conversion of diphenyl ether and guaiacol were investigated in the
vapour phase using Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO bimetallic catalysts under the disparate
o
o
experimental conditions (Temperature 370 C & 420 C, atmospheric hydrogen pressure 50
ꢀ1
ꢀ1
mL min , WHSV (h ) = 1.8, 3.6, & 5.4). Figure 8 (AꢀC) elucidated conversion and
o
selectivity of diphenyl ether for Rh/Ni/AlꢀKITꢀ6 catalyst under 370 C with three different
WHSV.
Figure 8 (A-C) Diphenyl ether conversion and selectivity with respect to timeꢀonꢀstream for
Rh/Ni/AlꢀKITꢀ6 catalyst
ꢀ1
°
2
Conditions: WHSV (h ) =1.8, 3.6, 5.4, atmosphere pressure, temperature=370 C, H =50
mL min .
ꢀ1
Figure 8 (A) showed maximum diphenyl ether conversion of 38 % and the selectivity
ꢀ1
of benzene shows 17 % at the lower WHSV of 1.8 h , initially the conversion was maximum
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8

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obtained and further increasing the time the trend was decreased. Similarly, Figure 8 (B) at
ꢀ1
WHSV 3.6 h displayed conversion and selectivity of diphenyl ether with the supreme
conversion 28 % was obtained initially, and further the conversion was decreased at higher
timeꢀonꢀstream. Besides, the selective product of benzene maximum 31 % was obtained at
ꢀ1
ꢀ1
WHSV of 3.6 h . Likewise Figure 8 (C) at WHSV 5.4 h showed highest diphenyl ether
conversion of 31 % with the benzene selectivity of 37 % and further the conversion trend was
decreased insignificantly as increasing the timeꢀonꢀstream. We observed that the above
o
experiment from Figure 8 (AꢀC) under the three different WHSV at 370 C for Rh/Ni/Alꢀ
KITꢀ6 catalyst shows maximum diphenyl ether conversion below 40 % and it represented
that the effect of WHSV did not significantly enhance the conversion of diphenyl ether and
o
the temperature of 370 C was not sufficient for obtaining higher conversion and selectivity.
o
Consequently, the reaction temperature was increased to 420 C
Figure 8 (D-F) Diphenyl ether conversion and selectivity with respect to timeꢀonꢀstream for
Rh/Ni/AlꢀKITꢀ6 catalyst
ꢀ1
°
2
Conditions: WHSV (h ) =1.8, 3.6, 5.4, atmosphere pressure, temperature=420 C, H =50mL
min .
ꢀ1
o
The conversion and selectivity of diphenyl ether at 420 C with three different WHSV
for Rh/Ni/AlꢀKITꢀ6 catalyst was shown in Figure 8 (DꢀF). Diphenyl ether conversion at 420
1
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o
ꢀ1
C with WHSV 1.8 h [Figure 8 (D)] shows the highest conversion of 28 % and selectivity of
benzene 39 %, on increasing the timeꢀonꢀstream, a slight decrease in conversion trend was
o
observed. However, on comparing the conversion trend with respect to temperature at 370 C
ꢀ1
under lower WHSV 1.8 h , the conversion about 10 % was decreased this may be due to the
higher temperature and lower WHSV conditions may not be suitable for obtaining higher
conversion and further decreased the conversion by strong adsorption of reactant molecule
leads to form faster coke deposition. However, Figure 8(E) showed conversion and selectivity
ꢀ1
of diphenyl ether at WHSV 3.6 h , the utmost conversion of diphenyl ether 63 % and the
highest selectivity of benzene 60 % with cyclohexanol 8 % was observed. Figure 8 (F)
ꢀ1
represented conversion and selectivity of diphenyl ether at WHSV 5.4 h and this condition
the conversion was maximum 37 % and selectivity of benzene 38 % was observed. The
o
optimum diphenyl ether conversion and benzene selectivity was identified at 420 C under
ꢀ1
moderate WHSV 3.6 h .
Figure 9(A-C) Guaiacol conversion and selectivity with respect to timeꢀonꢀstream for
Rh/Ni/AlꢀKITꢀ6 catalyst
ꢀ1
°
2
Conditions: WHSV (h ) =1.8, 3.7, 5.5, atmosphere pressure, temperature=420 C, H =50mL
min .
ꢀ1
The conversion and selectivity of guaiacol on Rh/Ni/AlꢀKITꢀ6 catalyst was illustrated
o
ꢀ1
in Figure 9 (AꢀC) under the condition of 420 C with three different WHSV (h ) 1.8, 3.7 &
2
0

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ꢀ1
5.5. The conversion and selectivity tendency of guaiacol under the lower WHSV 1.8 h
represented in Figure 9 (A), and it shows that the conversion of guaiacol maximum 39 %
with selectivity of mono oxygenated product of anisole maximum 44 %, phenol 32 %, 2ꢀ
methyl phenol 40 % and catechol selectivity 38 % was observed. Initially the conversion was
increased with increasing the timeꢀonꢀstream and it reaches maximum conversion still 9 h
and beyond the limit, conversion tends to decrease. Figure 9 (B) shows guaiacol conversion
ꢀ1
and selectivity at WHSV 3.7 h the maximum conversion and selectivity observed at 12 h
and it shows conversion of 36 % with maximum selectivity of phenol 56 %, 2ꢀmethyl phenol
49 %, 4ꢀmethyl phenol 37 %, anisole 12 % and catechol 43 % was observed. Similarly,
Figure 9 (C) shows the conversion and selectivity of guaiacol for Rh/Ni/AlꢀKITꢀ6 catalyst
ꢀ1
under the higher WHSV 5.5 h , here the conversion of guaiacol 15 % with the selectivity of
phenol maximum 34 %, 2ꢀmethyl phenol 47 %, 4ꢀmethyl phenol 59 %, anisole 17 % and
o
catechol 30 % was observed. The present experimental condition of 420 C with three
different WHSV, the conversion of guaiacol was obtained maximum at lower WHSV and
further on increasing the WHSV, the conversion decrease. Moreover, the product selectivity
of guaiacol for Rh/Ni/AlꢀKITꢀ6 catalyst significantly produce methylated product than
complete deoxygenated product of benzene. However, on comparing the guaiacol conversion
with respect to diphenyl ether, the guaiacol conversion was less than that of diphenyl ether. It
revealed that the conversion and selectivity mainly depend on nature of reactant; guaiacol has
6
0
two types of reactive sites, methoxyl and hydroxyl groups . However, guaiacol has been
converted via methoxyl CꢀO bond cleavage to produce catechol as the major intermediate and
further catechol deoxygenated through direct deoxygenation of hydroxyl group to produce
phenol. Furthermore, phenol directly obtained from guaiacol via demethoxylation, which was
insignificant path than catechol intermediate because the CꢀOCH
than that of OꢀCH and further it was confirmed by the equal distribution of catechol obtained
with respect to phenol
and further conversion of phenol into benzene was restricted, while methyl phenol formation
3
bond energy was higher
3
61–65
. Phenol was identified as the secondary product or intermediate
6
6–68
via methyl transfer was significantly observed
.
Figure 10 (A) represented conversion and selectivity of diphenyl ether for Rh/Ni/rꢀ
o
ꢀ1
GO catalyst at 420 C with WHSV 3.6 h , the maximum conversion of diphenyl ether 55 %
with selectivity of benzene 39 %, phenol 80 %, and cyclohexanol 5 % was observed. Figure
o
1
0 (B) illustrate conversion and selectivity of guaiacol for Rh/Ni/rꢀGO catalyst under 420 C
ꢀ1
with WHSV 3.7 h , the maximum conversion of guaiacol 40 % with selectivity of phenol 56
, 2ꢀmethyl phenol 25 %, 4ꢀmethyl phenol 40 %, anisole 2 % and trace amount of benzene
%
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1% was observed. The superior catalytic performance was observed over Rh/Ni/AlꢀKITꢀ6
acidic bimetallic catalyst than Rh/Ni/rꢀGO catalyst, apparently due to the interaction between
rhodium and nickel with acidic mesoporous support enhancing the adsorption properties of
reactant molecule and further enhanced the CꢀO bond cleavage of reactant molecule.
Moreover, the diffusion of product from mesoporous catalyst was accelerated more than that
of reduced graphene oxide supported catalyst as evidenced by the higher conversion of
diphenyl ether.
Figure 10 Conversion and selectivity of (A) diphenyl ether, (B) guaiacol with respect to
timeꢀonꢀstream for Rh/Ni/rꢀGO
ꢀ
1
°
Conditions: WHSV (h ) =3.6 & 3.7, atmosphere pressure, temperature=420 C, H =50 mL
2
ꢀ1
ꢀ1
min , diphenyl ether/guaiacol flow rate (mL h ) =1.0
Table 2 represents comparison between Rh/Ni/Al/KITꢀ6 activities with other reported
work in the literature under the different experimental condition. In Table 2, Rh/Ni/AlꢀKITꢀ6
shows highest diphenyl ether conversion of 63 % under atmospheric pressure. However, the
work reported by the others showed complete conversion, but they are all done the
experiment at higher hydrogen pressure and using high pressure reactor. Therefore,
minimizing hydrogen consumption in the HDO process has been considered as significant
factor for achieving higher diphenyl ether conversion.
2
2

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Table 2 Comparison of Rh/Ni/AlꢀKITꢀ6 activity with other literature
Temp.
Pres.
(atm)
Con.
(%)
Catalyst
Reactant
Reactor
Fixed bed
reactor
High pressure
autoclave
o
Ref.
(
C)
Rh/Ni/AlꢀKITꢀ6 Diphenyl ether
420
140
1
63
98
This Work
Rh/HꢀBeta
Rh/C
Diphenyl ether
39
2
Diphenyl ether Batch reactor
Diphenyl ether Parr reactor
80
5
6
100
100
18
19
Ni/SiO
2
120
High pressure
Diphenyl ether
Pd/C
190
80
39
5
92
100
84
20
21
23
autoclave
Rh/C
Diphenyl ether Batch reactor
High pressure
Diphenyl ether
Ni/ZrPO
4
180
5
autoclave
Autoclave
reactor
Ni/SiO2
Diphenyl ether
120
200
6
100
100
24
25
Raney Ni
Diphenyl ether Batch reactor
49
Diphenyl ether conversion for Rh/Ni bimetal supported catalyst and its possible
reaction pathway was represented in Figure 11.
Figure 11 Possible reaction routes for diphenyl ether deoxygenation over Rh/Ni bimetal
supported catalysts
The target product of benzene maximum 60 % was obtained and the direct ring
saturated product of cyclohexyl phenyl ether and dicyclohexyl phenyl ether was not identified
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under the present atmospheric pressure condition. Since the direct hydrogenation of diphenyl
ether was limited than hydrogenolysis pathway and the major hydrodeoxygenation route was
diphenyl ether hydrogenolysis into benzene and phenol. And further, hydrogenation of
benzene and phenol into cyclohexane and cyclohexanol was not highly observed due to the
obstruction of Rh/Ni sites by aromatic ring or hydroxyl group, this indicated that
2,69–71
hydrogenolysis was
a
significant class of reaction
.
At earlier stage the
hydrodeoxygenation of diphenyl ether conversion increases and further increasing the time,
conversion decreased and it revealed that hydrogenolysis of diphenyl ether was much faster
than subsequent benzene hydrogenation. Moreover, the percentage of phenol and benzene
was not regular for all the experimental conditions and the phenol percentage was highly
observed than that of benzene percentage and even though the highest benzene selectivity 60
%
was observed.
In continuation with Rh/Ni/AlꢀKITꢀ6 for diphenyl ether conversion, Rh/Ni/rꢀGO
catalyst follows the similar reaction sequence for diphenyl ether conversion (Figure 10 A).
However, the conversion maximum 55 % with benzene selectivity 39 % was observed, which
was less than that of Rh/Ni/AlꢀKITꢀ6 catalyst, it reveals that the acidic support play a crucial
role for diphenyl ether conversion by the strong interaction with Rh/Ni bimetallic
25,72,73
species
. In general, the HDO of lignin model compound converted via hydrogenationꢀ
7
4
deoxygenation or direct deoxygenation pathway . However, some reports recommended that
the bimetal catalysts could enhance the direct deoxygenation pathway than deoxygenationꢀ
7
5
hydrogenation pathway , more over the addition of Rh to Ni offers the possibility of direct
deoxygenation of diphenyl ether via hydrogenolysis of CꢀO bond to produce benzene and
phenol, although it could not produce significantly hydrogenated product of cyclohexanol and
cyclohexane under the atmospheric pressure condition. Obviously the acidic AlꢀKITꢀ6
support had great improvement for enhancing the benzene selectivity of 60 %. However, in
contrast to rꢀGO support had only metal component, which catalyse the hydrogenolysis bond
breaking slower than the bifunctional Rh/Ni/AlꢀKITꢀ6 catalyst. Despite, the hydrogenolysis
of CꢀO bond required bifunctional reactive sites i.e., acid and metal sites and further the
50,67,70
presence of higher acid sites on the catalyst may increases the HDO efficiency
. The
advantages of using bimetallic catalysts for diphenyl ether and guaiacol conversion was
apparently high and still the complete deoxygenation and hydrogenation in the case of
guaiacol conversion was restricted under the present experimental condition due to the loss of
active sites by condensation of secondary oxygenated product to form carbon deposition over
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4

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76
the catalyst surface . The coke deposition on the catalyst surface was studied by thermal
gravimetric analysis.
Figure 12 Thermal gravimetric analysis of coke deposited bimetallic catalysts for diphenyl
ether and guaiacol conversion after 15h onꢀstream
Figure 12 (AꢀD) shows thermogramme of Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO spent
bimetallic catalyst for diphenyl ether and guaiacol conversion. The coke deposition was
highly observed in guaiacol converted spent catalyst than diphenyl ether converted catalyst.
The amount of coke deposition for diphenyl ether converted spent Rh/Ni/AlꢀKITꢀ6 catalyst
was shows 5.1 %, while guaiacol converted spent Rh/Ni/Al/KITꢀ6 catalyst was shows 8.5 %.
However, the coke deposition for diphenyl ether converted spent Rh/Ni/rꢀGO catalyst was
shows 4.4 % and for guaiacol converted spent Rh/Ni/rꢀGO catalyst was shows 9.3 %. Also, it
represented that the nature of oxygen model substrate were crucial to catalyst deactivation
7
6
under the present experimental condition .
The reuse experiment was carried out to check the stability of bimetallic Rh/Ni/AlꢀKITꢀ6
o
ꢀ1
catalyst under the optimum reaction condition of 420 C with WHSV 3.6 h . The spent
o
catalyst was regenerated by calcination at 500 C for 6 h in air and reused for another
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catalytic experiment. The regenerated Rh/Ni/AlꢀKITꢀ6 catalyst was characterized by low and
high angle XRD, which was represented in Figure13.
Figure 13 Low and high angle XRD patterns of regenerated Rh/Ni/AlꢀKITꢀ6 bimetallic
catalyst
The low angle XRD confirmed the intact of mesoporous nature of Rh/Ni/AlꢀKITꢀ6
catalyst by retaining the (211) and (200) plane and further high angle XRD shows existence
of crystalline metal oxide phases.
Figure 14 Conversion and selectivity of diphenyl ether for regenerated Rh/Ni/AlꢀKITꢀ6
bimetallic catalyst
ꢀ1
°
ꢀ1
Conditions: WHSV (h ) = 3.6, atmosphere pressure, temperature=420 C, H =50mL min .
2
2
6

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The result was shown in Figure14, for diphenyl ether conversion with respect to
regenerated Rh/Ni/AlꢀKITꢀ6 bimetallic catalyst, the maximum conversion 63 % with benzene
selectivity 57 % was observed and it revealed that the regenerated catalyst could not
significantly altered the activity pattern with respect to fresh catalytic reaction. Though, a
variation in the product distribution was observed, which may be due to the redistribution of
Rh/Ni particles during the regeneration process.
Conclusions
In this study, Rh/Ni bimetal impregnated mesoporous Ia3d cubic and rꢀGO supported
catalysts were synthesised and consistently characterized by XRD, FTꢀIR, HRꢀTEM, N
2
sorption, NH ꢀTPD, H ꢀTPR, EDAX and ICPꢀOES techniques. The potential diphenyl ether
3
2
and guaiacol conversion were identified on Rh/Ni/AlꢀKITꢀ6 catalyst than non acidic Rh/Ni/rꢀ
GO catalyst due to their bifunctional activity (metal and acid function). Diphenyl ether
conversion maximum 63 % and benzene selectivity maximum 60 % was achieved on
o
ꢀ1
Rh/Ni/AlꢀKITꢀ6 catalyst at 420 C with WHSV 3.6 h . However, for guaiacol conversion
into benzene on Rh/Ni/AlꢀKITꢀ6 and Rh/Ni/rꢀGO catalyst was restricted due to the formation
of secondary oxygenated product. The maximum coke tolerance was observed in diphenyl
ether converted Rh/Ni bimetallic catalysts than guaiacol converted Rh/Ni bimetallic catalysts.
The higher oxygen functionality in guaiacol was the major cause for coke deposition, which
was not completely converted after secondary product formation. The Rh/Ni/AlꢀKITꢀ6
catalyst was regenerated and it was confirmed by low and high angle XRD. Further, their
catalytic activity of diphenyl ether shows similar conversion and selectivity with respect to
earlier catalytic reaction, which was demonstrating the stability of Rh/Ni/AlꢀKITꢀ6 catalyst.
Moreover, the presence of hydrogen spill over effect, acidic behaviour with higher dispersion
of Rh/Ni particles on this Rh/Ni/AlꢀKITꢀ6 catalyst could appear as auspicious applicant for
the CꢀO bond cleavage of diphenyl ether and guaiacol.
Acknowledgements
This work is financially supported by UGCꢀBSR New Delhi, India. The
instrumentation facility mainly contributed by department of Chemistry, IIT Madras,
Chennai. The laboratory facility provided by department of Chemistry, Anna University,
Chennai under DSTꢀFIST and UGCꢀDRS are gratefully acknowledged.
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