Zirconia catalysed acetic acid ketonisation for pre-treatment of biomass fast pyrolysis vapours

Article abstract of DOI:10.1039/c7cy02541f

Crude pyrolysis bio-oil contains significant quantities of carboxylic acids which limit its utility as a biofuel. Vapour phase ketonisation of organic acids contained within biomass fast-pyrolysis vapours offers a potential pre-treatment to improve the stability and energy content of resulting bio-oils formed upon condensation. Zirconia is a promising catalyst for such reactions, however little is known regarding the impact of thermal processing on the physicochemical properties of zirconia in the context of it's corresponding reactivity for the vapour phase ketonisation of acetic acid. Here we show that calcination progressively transforms amorphous Zr(OH)₄ into small tetragonal ZrO₂ crystallites at 400 °C, and subsequently larger monoclinic crystallites >600 °C. These phase transitions are accompanied by an increase in the density of Lewis acid sites, and concomitant decrease in their acid strength, attributed to surface dehydroxylation and anion vacancy formation. Weak Lewis acid sites (and/or resulting acid-base pairs) are identified as the active species responsible for acetic acid ketonisation to acetone at 350 °C and 400 °C, with stronger Lewis acid sites favouring competing unselective reactions and carbon laydown. Acetone selectivity is independent of acid strength.

Full text of DOI:10.1039/c7cy02541f

View Article Online
View Journal
Catalysis
Sc ience &
Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: H. Jahnagiri, A.
Osatiashtiani, J. Bennett, M. A. Isaacs, S. Gu, A. F. Lee and W. Karen, Catal. Sci. Technol., 2018, DOI:
1
0.1039/C7CY02541F.
Volume 6 Number 1 7 January 2016 Pages 1–308
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Catalysis
Science &
Technology
www.rsc.org/catalysis
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2044-4753
PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
rsc.li/catalysis

Page 1 of 9
C Pa l tea al ys se i sd So c ni eo nt c ae d &j u Ts et cmh an rog l ion gs y
View Article Online
DOI: 10.1039/C7CY02541F
Journal Name
ARTICLE
Zirconia catalysed acetic acid ketonisation for pre-treatment of
biomass fast pyrolysis vapours.
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
a
a
a
c
Hessam Jahangiri, Amin Osatiashtiani, James A. Bennett, Mark A. Isaacs, Sai Gu, Adam. F.
d
*d
Lee and Karen Wilson
DOI: 10.1039/x0xx00000x
Crude pyrolysis bio-oil contains significant quantities of carboxylic acids which limit its utility as a biofuel. Vapour phase
ketonisation of organic acids contained within biomass fast-pyrolysis vapours offers a potential pre-treatment to improve
the stability and energy content of resulting bio-oils formed upon condensation. Zirconia is a promising catalyst for such
reactions, however little is known regarding the impact of thermal processing on the physicochemical properties of
zirconia in the context of their corresponding reactivity for the vapour phase ketonisation of acetic acid. Here we show
www.rsc.org/
4 2
that calcination progressively transforms amorphous Zr(OH) into small tetragonal ZrO crystallites at 400 °C, and
subsequently larger monoclinic crystallites >600 °C. These phase transitions are accompanied by an increase in the density
of Lewis acid sites, and concomitant decrease in their acid strength, attributed to surface dehydroxylation and anion
vacancy formation. Weak Lewis acid sites (and/or resulting acid-base pairs) are identified as the active species responsible
for acetic acid ketonisation to acetone at 350 °C and 400 °C, with stronger Lewis acid sites favouring competing unselective
reactions and carbon laydown. Acetone selectivity is independent of acid strength.
1
3
3
corrosive (pH 2-3) and chemically unstable. Crude bio-oils
must therefore be upgraded to remove corrosive components
and stabilise them prior to any final hydrodeoxygenation step
Introduction
Concerns over energy security and demand, and the
parallel impact of CO emissions from fossil fuels on global
to enhance their calorific value.
2
14-16
Ketonisation,
involving the condensation of two acid
and H O (Scheme 1), and
involving the reaction of carboxylic acids with
warming are driving a quest to find sustainable low carbon
1
energy sources.
, 2
molecules to form a ketone, CO
2
2
Waste lignocellulosic (non-edible) biomass
1
7-19
esterification
is the only sustainable hydrocarbon source that can provide an
immediate environmentally-benign replacement for non-
2
renewable liquid transportation fuels. However, such
alcohols (already present or from external addition), are
promising routes to lower the acidity of crude bio-oil.
Ketonisation is advantageous since it can be conducted in the
vapor phase without additional reactants, thereby enabling a
catalyst bed close-coupled to the fast pyrolysis unit to remove
acids from pyrolysis vapour prior to condensation as a bio-
biomass-derived fuels are currently incompatible with existing
distribution infrastructure and vehicle engines, and require
catalytic upgrading to improve their physicochemical
3
, 4
properties prior to implementation.
Bio-oil production by fast pyrolysis
1
oil.
6, 20
5
,
6
In addition to reducing acidity, ketonisation also results
, hydrothermal
or gasification and subsequent Fischer–
7
,
8
9
in bio-oil deoxygenation and concomitant hydrocarbon chain
2
growth.
liquefaction,
Tropsch synthesis,
1
1
0,11
are the main thermochemical
technologies to convert lignocellulosic biomass into liquid
hydrocarbons. Fast pyrolysis bio-oils are complex mixtures of
oxygenated compounds comprising phenolics, furanics,
carboxylic acids and other small oxygenates, the composition
of which depends on biomass source and processing
Scheme 1. Acetic acid ketonisation.
6
, 12, 13
conditions.
The high oxygen content of crude bio-oil
Ketonisation is an established reaction in organic
2
results in a heating value half that of petroleum-derived fuels,
while the presence of carboxylic acids and small reactive
oxygenates (e.g. unsaturated aldehydes) renders the oils
0, 22
synthesis, which can take place over various polycrystalline
oxides including alkali earth metal oxides (e.g. MgO, BaO
2
3, 24
),
2
5, 26
16, 27, 28
29, 30
transition metal oxides (e.g. CeO
32, 33
, MnO2
, TiO2
,
2
1
4, 16, 31
34
), and actinide oxides (e.g. ThO ).
Fe O4
3
and ZrO2
2
23
Mixed oxides of Ni, Co and Cu and layered double hydroxides
of Zn/Al and Mg/Al have also been explored for carboxylic acid
3
5, 36
ketonisation.
Promising results have been reported for
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

C Pa l tea al ys se i sd So c ni eo nt c ae d &j u Ts et cmh an rog l ion gs y
Page 2 of 9
View Article Online
DOI: 10.1039/C7CY02541F
Journal Name
, TiO
ARTICLE
3
7-39
ZrO
and anionic vacancies. ZrO
promoted by alkali metal ion (such as K or Na ) to tune their for 4 h, with the resulting materials named ZrO
2
2
, and CeO
2
,
reflecting the presence of cationic
Zirconium hydroxide Zr(OH)
4
(MEL Chemicals XZO880/01)
2
0
2
catalysed ketonisation may be was calcined in static air at temperatures between 300-800 °C
+
+
2
(x), where x is
4
0
acid/base properties.
the calcination temperature.
Ketonisation proceeds via two distinct pathways depending
on the lattice energy of the metal oxide, with low lattice
energy (strong bases) forming stable carboxylates that
Catalyst characterisation
Phase identification was evaluated by wide angle XRD using
C) to a Bruker D8 Advance diffractometer and Cu K radiation
yield ketones, whereas high lattice energy oxides enable a between range 2θ = 10-80 ° with a step size of 0.04 °. The ratio
4
1
thermally decompose at elevated temperature (>420
°
α
2
0
lower temperature surface catalysed route.
Despite between tetragonal and monoclinic phases was calculated
extensive research, mechanistic aspects of heterogeneously from their principal reflections at 2θ=50.3 ° and 28.3 °
2
0
catalysed ketonisation are still
a
matter of debate.
respectively, with crystallite sizes determined by Scherrer
and Langmuir- analysis of the same reflections.
have both been proposed, with the Surface areas, pore size distributions and mesopore
latter more widely accepted. Ketonisation requires that one volumes were determined by N porosimetry using a
4
2
Mechanisms based on Eley-Rideal
2
3, 43
Hinshelwood models
4
4
2
acid molecule possesses an α-H-atom relative to the -COOH Quantasorb Nova 4000e porosimeter using Quantachrome
group, with subsequent enolate formation occurring through Novawin 11.0 software. Samples were outgassed in vacuo at
either α-H abstraction, or α-H migration via keto-enol 120 °C for 2 h prior to analysis, with specific surface areas
tautomerization. The resulting enolate is proposed to attack a calculated by applying the Brunauer–Emmet–Teller (BET)
0
second Lewis acid coordinated, monodentate acetate species model over the range P/P = 0.05-0.30 of the isotherm. Pore
to form a β-keto acid intermediate, which in turn decomposes size distributions and mesopore volumes were calculated by
1
4, 45
via CO
2
and H
2
O elimination to yield the ketone product.
applying the Barrett–Joyner–Halenda (BJH) model to the
Zirconia is an attractive metal oxide for acetic acid desorption branch of the isotherm.
ketonisation, owing to its corrosion resistance, amphoteric
XPS measurements were carried out using a Kratos Axis HSi
properties, and ability to stabilise undercoordinated cations photoelectron spectrometer equipped with
4
a
charge
0, 46
necessary for carboxylic acid coordination.
α
The phase and neutraliser and a Mg K X-ray source (hν = 1253.6 eV). Spectra
surface termination of zirconia may also be readily tuned to were recorded using an analyser pass energy of 20 eV and X-
optimise its corresponding surface chemistry and catalytic ray power of 225 W at a normal emission. Valence band
activity/selectivity. Recent studies suggest that ketonisation spectra were recorded on a Kratos Supra employing a
α
proceeds over zirconia via carboxylic acid adsorption in a monchromated Al K X-ray source (hν = 1486.7 eV). Spectral
monodentate conformation at coordinatively unsaturated Zr-O fitting was performed using CasaXPS version 2.3.14, with
2
-
pairs, with mildly basic O sites promoting α-H abstraction and binding energies corrected to the C 1s peak at 284.6 eV, and
enolate formation. Enolates subsequently couple with acetic high-resolution C 1s, O 1s and Zr 3d XP spectra fitted using a
4
+
20,
acid molecularly chemisorbed at an adjacent Zr Lewis site.
common Gaussian/Lorentzian line shape. Spectra were Shirley
exhibits a higher turnover rate (normalised background-subtracted and surface compositions quantified
per acid-base pair) compared to the tetragonal phase, by application of element and instrument specific response
4
7
Monoclinic ZrO
2
4
5
attributed to its enhanced basicity. However, the monoclinic factors. Errors in surface composition were estimated by
phase undergoes rapid deactivation, possibly due to facile varying the background subtraction procedure across
deprotonation of carboxylic acids and the attendant formation reasonable limits and re-calculating fits.
4
7
of inert bidentate carboxylates at Zr-O-Zr sites. Although
The carbon content of spent catalysts was measured using
2
-
mechanistic studies suggest that the higher basicity of O in a Thermo Scientific Flash 2000 organic elemental analyser
monoclinic zirconia should promote the critical α-H cleavage, calibrated to sulfanilamide, fitted with a Cu/CuO CHNS quartz
such strong basic sites are also more likely to deactivate on- tube and a TCD. Samples were prepared by adding ~10 mg
stream under mild reaction conditions (<400
°
C) due to catalyst and ~2 mg V
Despite these reports, Acid site loadings and strength were determined via n-
the relationship between Lewis acidity and ketonisation propylamine (Sigma Aldrich, ≥99 %) temperature programmed
2 5
O to tin crucibles.
4
8
2
adsorption of reactively-formed CO .
activity and selectivity over different ZrO
poorly established.
2
polymorphs remains reaction using a Mettler Toledo TGA/DSC 2 STARe system
connected to a Pfeiffer Vacuum ThermoStar GSD 301 T3
Herein we report on the relationship between the surface Benchtop Mass Spectrometer (MS). Propylamine adsorption
chemistry of tetragonal and monoclinic zirconia, notably acid was performed by dosing liquid n-propylamine onto pre-
strength and site density, and reactivity for the continuous weighed samples (1 ml/20 mg) in the TGA crucible cell. Excess
vapour phase ketonisation of acetic acid to acetone.
physisorbed propylamine was removed by drying in a vacuum
oven at 30 °C prior to sample loading in the TGA. Samples were
heated in the TGA furnace from 40 °C to 800 °C at a ramp rate
Experimental
-1
-1
2
of 10 °C.min under flowing N (40 ml.min ), with evolved
Catalyst preparation
gases analysed by MS to monitor the appearance of reactively
formed propene over the acid sites.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 2
Please do not adjust margins

Page 3 of 9
C Pa l tea al ys se i sd So c ni eo nt c ae d &j u Ts et cmh an rog l ion gs y
View Article Online
DOI: 10.1039/C7CY02541F
Journal Name
ARTICLE
DRIFT measurements of pyridine adsorption were carried
out by impregnation of the diluted samples (10 wt% in KBr) monitored by XRD. No crystalline phases were observed for
with neat pyridine. Excess physisorbed pyridine was removed calcination temperatures <300 C (Figure 1), suggesting the
in a vacuum oven at 30 °C overnight prior to sample loading in presence of either amorphous zirconia or crystallites <2 nm.
the environmental cell. DRIFT spectra of the pyridine-saturated However, calcination at 400 C resulted in weak reflections at
4
The phase composition of calcined Zr(OH) was first
°
°
samples were recorded at room temperature under vacuum 2θ=24.2 °, 28.3 °, 31.5 °, 34.3 °, 35.5 °, 40.9 °, 49.4 °, 50.2 °,
using a Nicolet Avatar 370 MCT with Smart Collector accessory, 60.2 °, and 62.9 °, characteristic of the monoclinic phase (m-
mid/near infrared source and a mercury cadmium telluride ZrO
MCT-A) photon detector at -196 °C. the tetragonal phase (t-ZrO
temperatures favoured m-ZrO . Volume-averaged crystallite
sizes revealed t-ZrO crystallites present ≤600 °C of 9-10 nm
Ketonisation of acetic acid was performed in a continuous diameter, whereas m-ZrO crystallites grew from 14.5 to 48
2
), and at 2θ=30.5 °, 35.2 °, 50.3 °, and 60 ° characteristic of
5
).
0
(
2
Higher calcination
2
Catalytic ketonisation
2
2
flow packed-bed reactor with online GC analysis. The reactor nm upon calcination between 400 °C and 800 °C (Table 1).
comprised a 1 cm o.d. quartz tube, within which the catalyst These temperature-dependent phase changes are consistent
bed was placed centrally and retained by quartz wool plugs. A with previous reports,ref and a consequence of the balance
3
constant catalyst bed volume of 4 cm was used in all between the lower surface energy of t-ZrO and higher
,
2
5
1
experiments, comprised of 200 mg of catalyst diluted with thermodynamic stability of bulk m-ZrO2. For low calcination
fused silica granules. The reactor tube was positioned in a temperatures, the surface energy contribution dominates due
temperature-programmable furnace with a thermocouple to the small crystallite size (9 nm), which favours the
placed in contact with the catalyst bed. Acetic acid (Sigma- tetragonal phase, whereas following higher temperature
Aldrich, ACS reagent, ≥ 99.7 %) was fed in a down-flow fashion treatment the bulk lattice energy of the larger crystallites
into the reactor using an Agilent 1260 Infinity Isocratic Pump present favours the monoclinic phase; crystallite sintering
-
1
and N as the carrier gas (50 ml.min ). All reactor lines were promotes a phase transition from t-ZrO2
2
→
m-ZrO2.
heated to 130 °C to prevent condensation, and a 1 cm
diameter metal tube packed with fused silica granules was
used to ensure acetic acid vaporisation before the reactor. For
product stream analysis, a Varian 3800 GC with a heated gas-
sampling valve, equipped with a BR-Q PLOT column (30 m x
0.53 mm i.d.), was employed. Acetone and acetic acid were
detected by flame ionisation detector (FID). The online GC was
calibrated for acetic acid and acetone by injecting 50 µl of
standard solutions through a switching valve. Each injection
was repeated 10 times and an average peak area taken.
Acetic acid conversion, and acetone yield and selectivity,
were calculated according to Equations 1-3.
ꢉ
ꢊꢋꢌꢍꢎꢏꢉꢊꢋꢌꢍ
ꢀ
ꢁꢂꢃꢄꢅꢆꢇꢁꢂ ꢈ
ꢐꢑ ꢐ100
ꢐꢑ 100
Equation 1
Equation 2
Equation 3
ꢉ
ꢊꢋꢌꢍ
ꢎ
ꢉ
ꢊꢋꢗꢘꢙꢚꢗ
ꢊꢋꢌꢍꢎꢏꢉꢊꢋꢌꢍ
ꢒꢄꢓꢄꢔꢕꢇꢃꢇꢕꢖ ꢈꢐꢉ
ꢝꢞꢟꢞꢠꢡꢢꢣꢢꢡꢤꢐꢑꢐꢥꢦꢉꢣꢞꢧꢨꢢꢦꢉ
ꢩꢪꢪ
ꢛꢇꢄꢓꢜ ꢈꢐ
where ꢂꢫꢠꢬꢭꢎ is the initial moles of acetic acid,ꢐꢂꢫꢠꢬꢭ is the
final moles acetic acid and ꢂꢫꢠꢞꢡꢦꢉꢞ represents the moles of
produced as acetone.
4
Figure 1. XRD patterns of Zr(OH) as a function of calcination temperature.
Acetone was the main product observed over all catalysts
at both 350 and 400
by GC-MS (Figure S1) as a secondary reaction product of
acetone, 2-propanediol 2-acetate. Other commonly
observed products such as isobutene, acetaldehyde or CH (as
°C. The primary by-product was identified
2
Porosimetry (Figure S2a) reveals all ZrO samples exhibited
type IV isotherms, characteristic of mesoporous materials,
attributed to the presence of interparticle voids formed during
50
1
4
zirconia precipitation.
BET surface areas decreased
4
9
a primary product of acetic acid decarboxylation) were
detected in trace amounts (< 1 %). Blank reactions showed no
acetic acid conversion without a zirconia catalyst.
significantly with increasing calcination temperature,
consistent with ZrO2 sintering into the large monoclinic
crystallites observed by XRD (Table 1). BJH pore size
distributions (Figure S2b) showed a concomitant increase in
the size of interparticle voids.
Results and Discussion
Catalyst characterisation
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

C Pa l tea al ys se i sd So c ni eo nt c ae d &j u Ts et cmh an rog l ion gs y
Page 4 of 9
View Article Online
DOI: 10.1039/C7CY02541F
Journal Name
ARTICLE
4
Table 1. Physicochemical properties of calcined Zr(OH) .
c
Crystallite size
/ nm
O:Zr
atomic
ratio
Acid site
Surface
Avg. pore
Acid site
d
a
b
Tetragonal:monoclinic
d
density
Strong:weak acid
Catalyst
area
diameter
c
loading
d
-
2
2
.
-1
ratio
-1
/ ꢀmol.m
site ratio
/
m g
/ nm
Tetragonal Monoclinic
/ mmol.g
2.7
2.3
2.2
2.2
ZrO
ZrO
ZrO
ZrO
a
2
2
2
2
(300)
(400)
(600)
(800)
b
276
190
38
10
d
3.4
3.4
5.9
8.0
-
9
-
-
0.68
2.5
2.2
3.4
4.0
34.7
5.5
14.5
18
0.25
0.11
0
0.42
10
-
0.13
1.4
48
0.04
1.6
c
e
BET, BJH, XRD, Propylamine adsorption/TGA-MS, XPS.
Surface analysis (Table 1 and Table S1) revealed a decrease
in the surface O:Zr atomic ratio from 2.3 to 1.6 with increasing
calcination temperature, ascribed to surface dehydroxylation
and the creation of anion vacancies; such vacancies are
(
a)
essential to impart Lewis acid character to ZrO
2
and proposed
1
5, 44, 45, 52
ZrO (800)
2
to play a crucial role in carboxylic acid ketonisation.
High-resolution O 1s spectra (Figure 2a), evidence two surface
species with binding energies of 529.5 and 531.5 eV for the
2 2
ZrO (300), characteristic of ZrO and Zr-OH respectively.
ZrO (600)
2
Calcination increase the ratio of surface oxide:hydroxyl,
consistent with surface dehydroxylation at high temperature
5
3-55
(
Figure S3).
evidenced two distinct chemical environments at 181.8 and
82.3 eV for the Zr 5d5/2 component (Figure 2b), attributed to
The Zr 3d spin-orbit split doublet also
ZrO (400)
2
1
4
+
Zr species in ZrO
intensity increased from 0.8
C, but was unchanged at higher temperature (again consistent
2
and Zr-OH respectively, whose relative
→
2 on calcining from 300 400
→
ZrO (300)
2
°
with dehydroxylation). The ratio of O 1s and Zr 3d oxide
components was independent of calcination temperature
538
533
528
523
Binding energy / eV
(
Table S1), in accordance with the non-reducible character of
5
large zirconia crystallites. Surface dehydroxylation following
6
calcination is also apparent from DRIFTS (Figure S4), wherein
-
1
the 3000-3800 cm bands associated with surface hydroxyls is
partially attenuated >300 °C.
(b)
Valence band XP spectra (Figure S5) also evidence a phase
ZrO (800)
2
transition from amorphous Zr(OH)
00 C calcination, apparent as a 0.4 eV increase in the valence
band energy maximum. The ZrO valence band is comprised of
4 2
to crystalline m-ZrO after
8
°
2
hybridised O 2p and Zr 4d states, and its position and width
depends on the symmetry and associated crystal field splitting
ZrO (600)
2
5
7
of the oxide. The increase in valence band energy maximum
is characteristic of oxygen vacancy formation coincident with
ZrO (400)
2
m-ZrO
2
high temperature crystallisation and oxygen vacancy
5
8, 59
segregation to grain boundaries,
which open up indirect-
band transitions. The generation of such vacancies and
accompanying Lewis acid sites is expected to facilitate the
ZrO (300)
2
2
0, 44, 60
adsorption of acetate anions.
1
88
186
184
182
180
178
The nature of acid sites was subsequently probed as a
function of calcination temperature by pyridine DRIFTS. Figure
S6 shows the resulting DRIFT spectra of all samples exhibit
Binding energy / eV
−
1
bands at 1445, 1490, and 1605 cm attributed to pyridine Figure 2. a) O 1s and b) Zr 3d spectra of Zr(OH)
4
as a function of calcination
5
bound to Lewis acid sites. No bands were observed at 1540
0
temperature
-1
-1
cm or 1638 cm , confirming the absence of any Brønsted
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 4
Please do not adjust margins

Page 5 of 9
C Pa l tea al ys se i sd So c ni eo nt c ae d &j u Ts et cmh an rog l ion gs y
View Article Online
DOI: 10.1039/C7CY02541F
Journal Name
ARTICLE
6
1
acidity. Corresponding TPD profiles of reactively-formed and 400 °C increased monotonically with calcination
propene (arising from propylamine decomposition) shown in temperature up to 800 °C (Figure 4). The ratio of weak:strong
Figure 3 show the acid strength evolves with calcination acid site densities from propylamine TPD mirrors the trend in
temperature. ZrO
368 C, associated with strong acid sites, most likely sensitive, and occurs preferentially over weak acid sites (or
originating from high-index facets or defects.
temperature calcination resulted in the emergence of a second Increasing the reaction temperature from 350 °C to 400 °C
desorption peak at 500 C, indicative of weaker Lewis acid only resulted in a small TOF enhancement, in agreement with
2
(300) exhibited a single propene desorption reactivity, demonstrating that ketonisation is structure-
~
°
6
2
4+ 2-
45
2
Higher unsaturated Zr -O acid-base pairs) present in m-ZrO .
°
6
8
sites. Acid site loadings and corresponding densities are shown previous reports. Lifetime studies at 400 °C evidenced limited
in Table 1, and reveal that calcination increases the total acid deactivation (<20 %) over 8.5 h on-stream in all cases (Figure
-
4.0 µmol.m S8). Deactivation may occur through site-blocking by strongly
site density (due to vacancy formation) from 2.5
→
2
47
,
associated with the emergence of weak acid sites (Figure bound bidentate acetate species and/or coke formation.
S7). The presence of weak and strong acid sites on ZrO has Element analysis confirmed the presence of significant carbon
previously been suggested by NH -TPD, which shows only a post-reaction, whose content was inversely proportional to
poorly resolved doublet desorption peak, and also by using calcination temperature (falling from 8 to 1 wt% for ZrO
2
3
6
3
2
(300)
(800) respectively), suggesting that strong acid sites
sites remains unchanged with calcination temperature, the present at the surface of t-ZrO were responsible for
stronger acid sites are observed to weaken with progressive unselective oligomerisation reactions. Although all catalysts
recrystallization of ZrO , evidenced by an increase in the exhibited similar decreases in their absolute conversion over
desorption temperature of reactively-formed propene. We the course of extended reaction, their relative deactivation
6
1
potentiometric titration. While the strength of the weak acid and ZrO
2
2
2
4
+
postulate that this weakening may reflect coupling of Zr
was proportional to their carbon content post-reaction (Figure
Lewis acid sites to basic O as Zr -O defect pairs. This S9), confirming carbon deposition as responsible for
hypothesis is supported by CO titration (Table S2) which deactivation. Powder XRD provided no evidence of sintering
2
-
4+ 2-
64
2
reveals that calcination also increases the base site density.
during ketonisation (Figure S10).
1
60
1
0
0
0
0
0
ZrO₂(300)
ZrO₂(400)
ZrO₂(600)
ZrO₂(800)
3
50 °C
400 °C
.8
.6
.4
.2
120
8
0
0
0
4
2
00 300 400 500 600 700
Desorption temperature / °C
300
400
600
800
Calcination temperature / °C
Figure 4. Correlation between TOFs (normalised per acid site) for acetic acid
ketonisation at 50 % iso-conversion and weak:strong acid site densities for
Figure 3. Reactively-formed propene TPD from propylamine chemisorbed over Zr(OH)
4
as a function of calcination temperature (normalised to surface area).
Zr(OH)
catalyst, 0.1-0.4 ml.min acetic acid, 50 ml.min
4
as a function of calcination temperature. Reaction conditions: 200 mg
-1 -1
2
N , and ambient pressure.
In summary, the phase transition from t- to m-ZrO
accompanies high temperature calcination of zirconia is
accompanied by surface dehydroxylation, anion vacancy temperature at ~32 % of the maximum theoretical value
2
that
Acetone selectivity was only weakly-dependent on reaction
6
1, 65, 66 67
formation, and the appearance of weak acid sites,
(Figure S11), however its production was directly proportional
to the weak acid site density as shown in Figure 5 at both
reaction temperatures. The principal by-product from GC-MS
was 1 2-propanediol 2-acetate (Figure S1), with only trace
isobutene detected.
Acetic acid ketonisation
Vapour phase acetic acid ketonisation was subsequently
investigated over calcined Zr(OH) in a fixed-bed continuous
4
flow reactor. Turnover frequencies (TOFs) normalised per acid
site determined at iso-conversion for reactions at both 350 °C
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

C Pa l tea al ys se i sd So c ni eo nt c ae d &j u Ts et cmh an rog l ion gs y
Page 6 of 9
View Article Online
DOI: 10.1039/C7CY02541F
Journal Name
ARTICLE
monoclinic crystallites >600 °C, whose size increases with
temperature. Pyridine titration showed that all zirconias were
pure Lewis acids, however propylamine temperature-
programmed desorption revealed that zirconia restructuring
was accompanied by an increase in the surface density of
Lewis acid sites, and concomitant decrease in their acid
strength. The emergence of new, weak Lewis acid sites >300 °C
correlates with surface dehydroxylation and anion vacancy
formation observed by photoelectron spectroscopy. Turnover
frequencies for vapour phase acetic acid ketonisation at 350 °C
and 400 °C mirror the evolution of surface acidity, with
acetone productivity directly proportional to the surface
density of weak Lewis acid sites; the latter (or their resulting
acid-base pairs) are therefore identified as the active catalytic
species for ketonisation. Strong Lewis acid sites favour
competing unselective reactions and carbon laydown,
although <20 % deactivation was observed for 8.5 h on-stream
in all cases, evidencing good stability for all calcined zirconias.
Acetic acid ketonisation thus offers an attractive route to
upgrade biomass-derived fast pyrolysis vapours through close-
coupling of zirconia catalysts possessing high densities of weak
Lewis acid sites and/or related acid-base pairs to the hot outlet
of a pyrolysis reactor.
9
8
7
0
0
0
2
1
1
1
1
1
0
8
6
4
2
0
8
6
3
4
50 °C
00 °C
60
5
4
3
2
1
0
0
0
0
0
0
0
0.5
1
1.5
2
Weak acid site density / ꢀmol.m-2
Figure 5. Acetone productivity from acetic acid ketonisation at 50 % ico-conversion for
Zr(OH) as a function of weak acid site density (calcination temperature). Reaction
4
-
1
-1
conditions: 200 mg catalyst, 0.1-0.4 ml.min acetic acid, 50 ml.min
2
N , and ambient
pressure.
Acknowledgements
Our observation that weak Lewis acid sites and/or related
acid-base pairs are the active species responsible for acetic We thank the EPSRC (EP/K036548/2, EP/K014676/1,
acid ketonisation to acetone in the vapour phase is consistent EP/N009924/1) for financial support. K.W. thanks the Royal
6
9-72
47
with previous experimental
and computational studies.
Society for the award of an Industry Fellowship. The work was
DFT calculations indicate that acetic acid may adopt several also conducted with support from the EU under the frame of
adsorption modes over zirconia shown in Scheme 2: molecular the FP7-funded CAScade deoxygenation process using tailored
acetic acid (I); monodentate acetate (II); or as bridging, nanoCATalysts for the production of BiofuELs from
4
7
bidentate acetate (III).
Recent reports suggest that lignocellullosic biomass (CASCATBEL) project (Grant
ketonisation preferentially proceeds via a reaction between Agreement No. 604307). MEL Chemicals are thanked for the
molecular (I) and monodentate (II) species, bound at adjacent provision of Zr(OH)4.
acid-base pairs. The development of high performance
ketonisation catalysts therefore requires new synthetic routes
Notes and references
2
to prepare (and stabilise) high area m-ZrO nanoparticles,
possessing higher densities of weak Lewis acid sites to enhance
selectivity to acetone at lower reaction temperatures.
1
1
2
2
3
2
4
. M. Z. Jacobson, Energy & Environmental Science, 2009,
2
,
,
48-173.
. K. Wilson and A. F. Lee, Phil. Trans. R. Soc. A, 2016, 374
0150081.
. D. M. Alonso, J. Q. Bond and J. A. Dumesic, Green Chemistry,
010, 12, 1493-1513.
. W. Leitner, J. Klankermayer, S. Pischinger, H. Pitsch and K.
Kohse-Höinghaus, Angewandte Chemie International Edition,
2
Scheme 2. Surface species formed upon adsorption of acetic acid on ZrO .
2
5
6
7
2
8
017, 56, 5412-5452.
. A. V. Bridgwater, Biomass Bioenerg, 2012, 38, 68-94.
. A. V. Bridgwater, Environ Prog Sustain, 2012, 31, 261-268.
. S. S. Toor, L. Rosendahl and A. Rudolf, Energy, 2011, 36
328-2342.
Conclusions
,
The evolution of structural and acidic properties of zirconia
nanocatalysts was therefore investigated as a function of
calcination temperature to elucidate underlying structure-
reactivity relations in acetic acid ketonisation. Powder XRD
. D. C. Elliott, P. Biller, A. B. Ross, A. J. Schmidt and S. B. Jones,
Bioresource Technology, 2015, 178, 147-156.
. M. M. Yung, W. S. Jablonski and K. A. Magrini-Bair, Energy &
Fuels, 2009, 23, 1874-1887.
9
evidenced that calcination of amorphous Zr(OH)
4
resulted in
the crystallisation of small (~9 nm) t-ZrO particles at 400 °C,
2
and a subsequent phase transition to larger (15-48 nm)
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 6
Please do not adjust margins

Page 7 of 9
C Pa l tea al ys se i sd So c ni eo nt c ae d &j u Ts et cmh an rog l ion gs y
View Article Online
DOI: 10.1039/C7CY02541F
Journal Name
ARTICLE
1
0. H. Jahangiri, J. Bennett, P. Mahjoubi, K. Wilson and S. Gu, 36. K. Parida and J. Das, Journal of Molecular Catalysis A:
Catal Sci Technol, 2014,
4
, 2210-2229.
Chemical, 2000, 151, 185-192.
1
1. S. Sartipi, M. Makkee, F. Kapteijn and J. Gascon, Catal Sci 37. M. Glinski and J. Kijenski, Appl Catal a-Gen, 2000, 190, 87-91.
Technol, 2014,
4, 893-907.
38. M. I. Zaki, M. A. Hasan and L. Pasupulety, Langmuir, 2001,
1
2. T. Sfetsas, C. Michailof, A. Lappas, Q. Li and B. Kneale, 17, 768-774.
Journal of Chromatography A, 2011, 1218, 3317-3325. 39. M. I. Zaki, M. A. Hasan, F. A. Al-Sagheer and L. Pasupulety,
3. L. Ciddor, J. A. Bennett, J. A. Hunns, K. Wilson and A. F. Lee, Colloid Surface A, 2001, 190, 261-274.
Journal of Chemical Technology & Biotechnology, 2015, 90, 780- 40. K. Parida and H. K. Mishra, Journal of Molecular Catalysis A:
1
7
1
95.
Chemical, 1999, 139, 73-80.
4. J. A. Bennett, C. M. A. Parlett, M. A. Isaacs, L. J. Durndell, L. 41. K. C. Patil, G. V. Chandrashekhar, M. V. George and C. N. R.
Olivi, A. F. Lee and K. Wilson, ChemCatChem, 2017,
9, 1648- Rao, Canadian Journal of Chemistry, 1968, 46, 257-265.
1
1
2
1
654.
42. A. V. Ignatchenko and E. I. Kozliak, Acs Catal, 2012, 2, 1555-
5. T. N. Pham, D. Shi and D. E. Resasco, Topics in Catalysis, 1562.
014, 57, 706-714. 43. Y. Yamada, M. Segawa, F. Sato, T. Kojima and S. Sato, Journal
6. E. Heracleous, D. Gu, F. Schüth, J. A. Bennett, M. A. Isaacs, A. of Molecular Catalysis A: Chemical, 2011, 346, 79-86.
, 2874-2888.
45. S. Wang and E. Iglesia, J Catal, 2017, 345, 183-206.
7. A. Osatiashtiani, B. Puértolas, C. C. S. Oliveira, J. C. Manayil, 46. S. Tosoni and G. Pacchioni, J Catal, 2016, 344, 465-473.
F. Lee, K. Wilson and A. A. Lappas, Biomass Conversion and 44. G. Pacchioni, Acs Catal, 2014,
Biorefinery, 2017, , 319-329.
4
7
1
B. Barbero, M. Isaacs, C. Michailof, E. Heracleous, J. Pérez- 47. S. Wang and E. Iglesia, The Journal of Physical Chemistry C,
Ramírez, A. F. Lee and K. Wilson, Biomass Conversion and 2017, 121, 18030-18046.
Biorefinery, 2017,
8. J. C. Manayil, A. Osatiashtiani, A. Mendoza, C. M. A. Parlett, 2016, 652, 163-171.
M. A. Isaacs, L. J. Durndell, C. Michailof, E. Heracleous, A. Lappas, 49. M. A. Hasan, M. I. Zaki and L. Pasupulety, Applied Catalysis A:
A. F. Lee and K. Wilson, ChemSusChem, 10, 3506-3511. General, 2003, 243, 81-92.
9. J. C. Manayil, C. V. M. Inocencio, A. F. Lee and K. Wilson, 50. A. Osatiashtiani, A. F. Lee, D. R. Brown, J. A. Melero, G.
Green Chemistry, 2016, 18, 1387-1394. Morales and K. Wilson, Catal Sci Technol, 2014, , 333-342.
0. T. N. Pham, T. Sooknoi, S. P. Crossley and D. E. Resasco, Acs 51. T. Chraska, A. H. King and C. C. Berndt, Materials Science and
Catal, 2013, , 2456-2473. Engineering: A, 2000, 286, 169-178.
1. C. A. Gaertner, J. C. Serrano-Ruiz, D. J. Braden and J. A. 52. V. N. Panchenko, Y. A. Zaytseva, M. N. Simonov, I. L.
7, 331-342.
48. H.-Y. T. Chen, S. Tosoni and G. Pacchioni, Surface Science,
1
1
4
2
3
2
Dumesic, Industrial & Engineering Chemistry Research, 2010, 49
,
Simakova and E. A. Paukshtis, Journal of Molecular Catalysis A:
Chemical, 2014, 388, 133-140.
6
2
2
027-6033.
2. , Google Patents, 1938.
53. R. Brenier, J. Mugnier and E. Mirica, Appl Surf Sci, 1999, 143
,
3. O. Nagashima, S. Sato, R. Takahashi and T. Sodesawa, Journal 85-91.
of Molecular Catalysis A: Chemical, 2005, 227, 231-239.
54. M. Hino, M. Kurashige, H. Matsuhashi and K. Arata,
2
4. R. Pestman, R. M. Koster, A. vanDuijne, J. A. Z. Pieterse and Thermochim Acta, 2006, 441, 35-41.
V. Ponec, J Catal, 1997, 168, 265-272.
55. S. Tsunekawa, K. Asami, S. Ito, M. Yashima and T. Sugimoto,
2
5. S. D. Randery, J. S. Warren and K. M. Dooley, Appl Catal a- Appl Surf Sci, 2005, 252, 1651-1656.
Gen, 2002, 226, 265-280.
56. M. C. Deibert and R. Kahraman, Appl Surf Sci, 1989, 37, 327-
2
6. K. M. Dooley, A. K. Bhat, C. P. Plaisance and A. D. Roy, Appl 336.
Catal a-Gen, 2007, 320, 122-133.
57. L. Soriano, M. Abbate, J. Faber, C. Morant and J. M. Sanz,
2
7. M. Gliński and J. Kijeński, Reaction Kinetics and Catalysis Solid State Communications, 1995, 93, 659-665.
Letters, 2000, 69, 123-128.
58. S.-m. Chang and R.-a. Doong, Chemistry of Materials, 2007,
2
8. K. M. Parida, A. Samal and N. N. Das, Applied Catalysis A: 19, 4804-4810.
General, 1998, 166, 201-205.
59. S.-m. Chang and R.-a. Doong, Chemistry of Materials, 2005,
17, 4837-4844.
2
4
3
3
9. R. Martinez, M. C. Huff and M. A. Barteau, J Catal, 2004, 222,
04-409.
60. Y. Lee, J.-W. Choi, D. J. Suh, J.-M. Ha and C.-H. Lee, Applied
Catalysis A: General, 2015, 506, 288-293.
0. K. S. Kim and M. A. Barteau, J Catal, 1990, 125, 353-375.
1. R. Pestman, R. M. Koster, J. A. Z. Pieterse and V. Ponec, J 61. H. M. Altass and A. E. R. S. Khder, Journal of Molecular
Catalysis A: Chemical, 2016, 411, 138-145.
2. M. Gliński and J. Kijeński, Applied Catalysis A: General, 2000, 62. C. Morterra, G. Cerrato, L. Ferroni, A. Negro and L.
Catal, 1997, 168, 255-264.
3
1
3
3
90, 87-91.
Montanaro, Appl Surf Sci, 1993, 65, 257-264.
3. K. Okumura and Y. Iwasawa, J Catal, 1996, 164, 440-448.
63. H.-J. Eom, M.-S. Kim, D.-W. Lee, Y.-K. Hong, G. Jeong and K.-
4. S. S. Kistler, S. Swann and E. G. Appel, Industrial & Y. Lee, Applied Catalysis A: General, 2015, 493, 149-157.
64. K. T. Jung and A. T. Bell, Journal of Molecular Catalysis A:
5. J. Das and K. Parida, Reaction Kinetics and Catalysis Letters, Chemical, 2000, 163, 27-42.
Engineering Chemistry, 1934, 26, 388-391.
3
2
000, 69, 223-229.
65. S. Makoto, T. Kyoko, K. Hideyuki and M. Hajime, Bulletin of
the Chemical Society of Japan, 1990, 63, 258-259.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

C Pa l tea al ys se i sd So c ni eo nt c ae d &j u Ts et cmh an rog l ion gs y
Page 8 of 9
View Article Online
DOI: 10.1039/C7CY02541F
Journal Name
ARTICLE
6
4
6
6. K. Pokrovski, K. T. Jung and A. T. Bell, Langmuir, 2001, 17
297-4303.
7. V. Bolis, C. Morterra, M. Volante, L. Orio and B. Fubini,
, 695-701.
8. A. Pulido, B. Oliver-Tomas, M. Renz, M. Boronat and A.
Corma, ChemSusChem, 2013, , 141-151.
9. A. Mattsson and L. Österlund, The Journal of Physical
Chemistry C, 2010, 114, 14121-14132.
0. Q. Ma, Y. Liu, C. Liu and H. He, Physical Chemistry Chemical
Physics, 2012, 14, 8403-8409.
1. E. Finocchio, R. J. Willey, G. Busca and V. Lorenzelli, Journal
of the Chemical Society, Faraday Transactions, 1997, 93, 175-
,
Langmuir, 1990,
6
6
6
6
7
7
1
7
80.
2. A. C. Geiculescu and H. G. Spencer, Journal of Sol-Gel Science
and Technology, 2000, 17, 25-35.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 8
Please do not adjust margins

Page 9 of 9
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C7CY02541F
7
8x39mm (150 x 150 DPI)