Solid base catalysed 5-HMF oxidation to 2,5-FDCA over Au/hydrotalcites: fact or fiction?

Article abstract of DOI:10.1039/c5sc00854a

Nanoparticulate gold has emerged as a promising catalyst for diverse mild and efficient selective aerobic oxidations. However, the mechanism of such atom-economical transformations, and synergy with functional supports, remains poorly understood. Alkali-free Mg-Al hydrotalcites are excellent solid base catalysts for the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furan dicarboxylic acid (FDCA), but only in concert with high concentrations of metallic gold nanoparticles. In the absence of soluble base, competitive adsorption between strongly-bound HMF and reactively-formed oxidation intermediates site-blocks gold. Aqueous NaOH dramatically promotes solution phase HMF activation, liberating free gold sites able to activate the alcohol function within the metastable 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) reactive intermediate. Synergistic effects between moderate strength base sites within alkali-free hydrotalcites and high gold surface concentrations can afford highly selective and entirely heterogeneous catalysts for aqueous phase aldehyde and alcohol cascade oxidations pertinent to biomass transformation.

Full text of DOI:10.1039/c5sc00854a

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ARTICLE
Solid base catalysed 5-HMF oxidation to 2,5-FDCA
over Au/hydrotalcites: Fact or fiction?
Cite this: DOI: 10.1039/x0xx00000x
Leandro Ardemani,a Giannantonio Cibin,b Andrew J. Dent,b Mark A. Isaacs,a
Adam F. Lee,a* Christopher M.A. Parlett,a Stephen A. Parryb and Karen Wilsonc*
Received 00th January 2012,
Accepted 00th January 2012
Nanoparticulate gold has emerged as a promising catalyst for diverse mild and efficient
selective aerobic oxidations. However, the mechanism of such atomꢀeconomical
transformations, and synergy with functional supports, remains poorly understood. Alkaliꢀfree
MgꢀAl hydrotalcites are excellent solid base catalysts for the aerobic oxidation of 5ꢀ
hydroxymethylfurfural (HMF) to 2,5ꢀfuran dicarboxylic acid (FDCA), but only in concert with
high concentrations of metallic gold nanoparticles. In the absence of soluble base, competitive
adsorption between stronglyꢀbound HMF and reactivelyꢀformed oxidation intermediates siteꢀ
blocks gold. Aqueous NaOH dramatically promotes solution phase HMF activation, liberating
free gold sites able to activate the alcohol function within the metastable 5ꢀhydroxymethylꢀ2ꢀ
furancarboxylic acid (HMFCA) reactive intermediate. Synergistic effects between moderate
strength base sites within alkaliꢀfree hydrotalcites and high gold surface concentrations can
afford highly selective and entirely heterogeneous catalysts for aqueous phase aldehyde and
DOI: 10.1039/x0xx00000x
www.rsc.org/
alcohol cascade oxidations pertinent to biomass transformation
.
Biomass offers the most readily implemented, and low cost, metal halides (Co/Mn/Br)21 which necessitate harsh (70 bar)
sustainable ‘dropꢀin’ alternative to existing fossil fuelꢀderived and corrosive conditions and poor atom efficiencies due to
transportation fuels,1 and the only nonꢀpetroleum route to significant waste generation during product purification. In the
organic molecules essential to the manufacture of bulk, fine and past five years, gold nanoparticles supported on reducible metal
speciality chemicals and polymers2 required to meet future oxides
(Au/TiO2,6
Au/CeO2 ,
AuꢀCu/TiO2
and
7
22
societal demands.3, 4 The development of biorefineries offering Au/Ce1−xBixO2− 23) have been reported to catalyse the aerobic
δ
the coꢀproduction of fuels, chemicals and energy,5 analogous to oxidation of HMF to FDCA, but require the addition of 1–20
current petroleum refineries which deliver high volume/low equiv. soluble base to accelerate alkoxide formation and CꢀH
value (fuels and commodity chemicals) and low volume/high activation in the catalytic cycle. Indeed, a requirement for base
value (fine/speciality chemicals) products, will underpin addition has emerged as a general phenomenon in gold
commercial exploitation of the biomass feedstocks. In this catalysed alcohol oxidations,24, 25 and processing the attendant
respect, the US DoE has identified 12 platform chemicals aqueous waste stream resulting from subsequent acidification
obtainable through sugars via the (bio)chemical transformation and purification of the reaction mixture8 presents a serious
of lignocellulosic biomass. 2,5ꢀFuran dicarboxylic acid (FDCA) barrier to commercialization.26 A recent report suggests that
is one of the key near market platform chemicals with an bimetallic AuPd nanoparticles supported on carbon nanotubes
estimated value of $50.5 billion, and is viewed as a potential may obviate the requirement for basicity, although reaction is
replacement for terephthalic acid in various polyesters and an slow and proceeds under high p
O2.27 Solid base supports may
intermediate to other polymers, fine chemicals, pharmaceuticals circumvent the need for liquid base addition,28ꢀ30 with Au/Mgꢀ
and agrochemicals.6ꢀ10 Heterogeneous catalysis and process Al hydrotalcites (HT) reported as effective for FDCA
engineering are pivotal to realizing the potential of production from HMF under an atmospheric oxygen pressure,31
lignocellulosic biomass for the production of such renewable or using a biphasic solvent system over AuPd/HT albeit it in the
chemicals11ꢀ16 underpinned by the rational design of presence of additional Na2CO3.32 However, despite the topical
multifunctional tailored catalysts able to affect cascade and nature of Au catalysis, the role of basic supports in aqueous
telescopic reactions at mild temperatures in the aqueous phase.
phase oxidations,33 and potential contribution of homogeneous
A promising route to FDCA is via the aerobic selective base on observed performance,24, 34, 35 remains hotly debated.25,
33, 36ꢀ39
oxidation of 5ꢀhydroxymethylfurfural (HMF), which in turn
may be derived from cellulose
This in part reflects the synthetic methodologies often
through employed to synthesise inorganic basic supports such as
isomerisation/dehydration of hexoses.17ꢀ20 The stepwise hydrotalcites, notably precipitation with Na2CO3/NaOH,31
heterogeneously catalysed transformation of HMF to FDCA which result in contamination by soluble alkali residues.40ꢀ42
using molecular oxygen is highly desirable,8 obviating the need This uncertainty in turn hampers elucidation of the role played
for stoichiometric oxidants such as KMnO4 or homogeneous by basic supports within catalytic oxidation cycles.
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Fig. 1 In-situ Au LIII XANES during thermal processing of the HAuCl4/Mg-Al HT precursor: a) thermal evolution of normalised XANES spectra; b) representative least
squares fitted XANES spectra to reference gold species; c) quantitative thermal evolution of fitted Au species.
Herein we show that the selective aerobic oxidation of HMF
to FDCA over gold nanoparticles on an alkaliꢀfree hydrotalcite
carrier exhibits unusual and unexpected sensitivity to the
surface concentration of metallic gold. Specifically, kinetic and
operando spectroscopic studies reveal that low concentrations
of surface gold require liquid base in order to overcome rateꢀ
limiting competitive adsorption and effect oxidation of reaction
intermediates. In contrast, high gold concentrations can achieve
high yields of FDCA over a solid base alone. This interplay
between reactants and intermediates at different reaction centres
within bifunctional catalysts has profound implications for
heterogeneously catalysed cascades.
Atmospheric pressure HMF aerobic oxidation over the
resultant 200 C calcined 2 wt% Au/HT in the absence of
°
additional NaOH proceeded efficiently (conversions >80 %,
Fig. 2), but was only selective to 5ꢀhydroxymethylꢀ2ꢀ
furancarboxylic acid (HMFCA) resulting from oxidation of the
carbonyl function.† Further oxidation to 5ꢀformylꢀ2ꢀfuran
carboxylic acid (FFCA) and the desired FDCA product was
slow, contrary to an earlier report using a comparable 2 wt%
Au catalyst prepared on an alkaliꢀprecipitated MgꢀAl HT,
wherein near quantitative yields of FDCA were reported under
identical reaction conditions 31. This discrepancy highlights an
important role for soluble base in activating RꢀOH functions
over Au, arising either from alkali contaminants leached from
Na2CO3/NaOH precipitated hydrotalcites, or partially soluble
brucite coꢀexisting with the hydrotalcite. Sensitivity towards
potential leachates was quantified through deliberate spiking of
our alkaliꢀfree Au/HT catalysed oxidations with additional
parent MgꢀAl HT (pH = 9), or Mg(OH)2 (pH = 10) or NaOH
To perform a comprehensive study, a series of Au/HT
catalyst materials were prepared using an alkaliꢀfree coꢀ
precipitation of the MgꢀAl hydrotalcite support,43 and
subsequent depositionꢀprecipitation of HAuCl4. In order to
optimise the catalyst synthesis, thermal evolution of the gold
precursor was investigated by inꢀsitu Au LIII Xꢀray absorption
near edge spectroscopy (XANES) (Fig. 1). XANES spectra of
the asꢀprepared materials are consistent with the presence of a
nꢀ
Au(III) salt, possibly Au(NHx)y(OH)z which may form during
depositionꢀprecipitation with ammonia or urea,44, 45 and ~10% (pH 14). Additional HT had negligible impact on FDCA
of Au(OH)3. Heating to 65 °C under flowing air initiated
precursor decomposition and the concomitant appearance of
Au2O3, which remained stable to ~110 °C before decomposing
to metallic Au. Complete decomposition of both the
Au(NHx)y(OH)znꢀ precursor and Au2O3 to metallic gold required
calcination >170 °C. The corresponding Extended Xꢀray
Absorption Fine Structure (EXAFS) for a 2 wt% Au/HT
calcined at 200 °C yielded a nearest neighbour AuꢀAu
production, while even 3 equiv. of Mg(OH)2 only increased the
FDCA yield to 38 % (Fig. S2), eliminating the possiblity that
surface brucite present in high Mg content hydrotalcites could
account for the literature value approaching 100 % dicarboxylic
acid over alkaliꢀprecipitated hydrotalcites. In contrast, raising
the pH via NaOH addition induced a progressive increase in
HMF conversion, accompanied by a dramatic switchover in
selectivity at pH>12.5 from HMFCA to FDCA (Fig. 2).
Additional soluble base is thus essential for efficient activation
coordination of 10.6 (Fig. S1 and Table S1), consistent with 4.2
47
nm diameter metal nanoparticles,46,
HRTEM, XRD and XPS (Figs. S2ꢀ4).
in agreement with
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of HMF (and the resultant reactivelyꢀ formed HMFCA) for this
particular HMF: surface gold ratio. As we show, later this
conclusion cannot be generalised to all substrate:catalyst ratios.
A plausible pH dependent reaction mechanism is illustrated in
Fig. 2. While not the subject of our present report, we note that
the basicity of our alkaliꢀfree hydrotalcite is a strong function of
thermal processing, with higher temperature calcination or
calcinationꢀrehydration treatments43 increasing the proportion
of strong base sites and corresponding rate of HMF oxidation.
Scheme 1 Impact of NaOH on kinetics of HMF oxidation over 2 wt% Au/HT.
The absence of 2,5ꢀdihydroxymethylfurfural (DHMF)
indicates that the competing base catalysed Cannizzaro reaction
50, wherein the geminal diol disproportionates to HFMCA and
DHMF in the solution phase, does not operate in the presence
of Au (or that DHMF oxidation is always extremely rapid).
HMFCA oxidation is clearly identified as the slowest step in
HMF oxidation, but while this step is indeed promoted by
soluble base, the greatest impact of NaOH is actually upon
HMF oxidation and the attendant increase in HMFCA
concentration, a discovery we return to shortly.
The question arises as to nature of the gold active phase
under such high pH conditions, and possibility of metal
leaching, oxidation or NaꢀAu intermetallic formation. This was
explored through an operando XAS study of aqueous phase
HMF aerobic oxidation over the preceding 2 wt% Au/HT
catalyst at 90 °C (Fig. 3). XANES analysis revealed that gold
remained in metallic form before and after NaOH addition, with
no evidence for Au(OH)3 formation, while EXAFS analysis
identified only AuꢀAu coordination shells with a constant
coordination number Table S1). These observations confirm
that gold nanoparticles do not sinter or leach even after 16 h
reaction, and that NaOH directly promotes oxidation without
influencing the electronic or structural properties of gold. This
is consistent with isotopeꢀlabelling and DFT studies,37, 49 which
suggest that hydroxyls adsorbed at the edge of Au clusters are
the critical surface species participating in the catalytic cycle,
lowering the barriers to CꢀH and OꢀH dissociation51 and
removing surface hydride.
Fig. 2 pH dependence of HMF oxidation over a 2 wt% Au/HT catalyst after 7 h
reaction, and possible mechanism for surface-initiated HMFCA at pH 9, and
solution phase activation at higher pH.
In order to elucidate the origin of this striking pH
sensitivity, we have comprehensively mapped the kinetics of
individual steps in the reaction pathway with and without
NaOH (6 mmols/pH 14). The results are summarised in Scheme
1. In accordance with conventional wisdom, which holds that
alcohols are oxidized more slowly than aldehydes over gold,25,
48
HMFCA
→FFCA (step 2) exhibited the slowest rate
with/without additional base and highest activation energy (40
kJ.molꢀ1). However, the aldehyde oxidations in steps 1 and 3
surprisingly exhibited the strongest NaOH dependencies,
equating to 100ꢀfold (HMF
(FFCA FDCA) rate enhancements respectively. These far
exceed the comparatively small fourꢀfold enhancement
observed for step 2 (HMFCA FFCA); this appears a general
→HMFCA) and 8ꢀfold
→
→
phenomenon for Au catalysed aldehyde versus alcohol
oxidation (Fig. S3). We attribute the dramatic impact of soluble
base upon HMF oxidation to its consequent displacement of the
equilibriumꢀlimited, geminal diol reactive intermediate towards
HMFCA;49 oxidation of the HMF aldehyde function to the
geminal diol is facile, however at lowꢀmoderate pH the reverse
dehydration is favoured.
Fig. 3 Operando Au LIII-edge XAS of a 2 wt% Au/HT catalyst during aqueous phase
selective aerobic oxidation of HMF; catalytically active, metallic gold
nanoparticles are unaffected by hot water or NaOH addition.
Fig. 2 demonstrates that alkaliꢀfree 2 wt% Au/HT is able to
oxidise HMF to FDCA (albeit slowly in the absence of soluble
base), while Scheme 1 highlights the principal role of NaOH as
to accelerate HMF oxidation to HMFCA, at least partially
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through suppressing dehydration of the reactivelyꢀformed HMFCA
→
FFCA and FFCA hydration/dehydrogenation to
geminal diol intermediate. The latter discovery led us to FDCA. In contrast, the HMF:surface Au molar ratio is only 5:1
speculate that the overall oxidation cascade could alternatively for the 10 wt% Au/HT catalyst, and one may therefore
be promoted through enhancing the rate of surface catalysed anticipate that the geminal diol faces significantly less
geminal diol dehydrogenation in steps 1 and 3 to corresponding competition from HMF for vacant gold sites. These hypotheses
carboxylic acids simply by increasing the Au concentration. A are supported by the strong nonꢀlinear dependence of FDCA
series of Au/HT catalysts were therefore synthesised employing production on HMF conversion (Fig. 5 main). FDCA requires a
a common, alkaliꢀfree MgꢀAl HT support with varying gold threshold HMF conversion >80 %, indicating that high
loadings (Table S2 and Figs. S4ꢀ8) which exhibited similar concentrations of reactivelyꢀformed HMFCA from the first
solid base strengths and site densities (Figs. S9ꢀ11). Fig. 4 oxidation step are necessary to compete effectively with
shows that higher gold loadings indeed promoted FDCA unreacted HMF for subsequent oxidation. In contrast, FDCA
production (at the expense of HMFCA), with a 78 % yield of production via the direct aerobic oxidation of HMFCA is near
the desired dicarboxylic acid attainable for 10 wt% Au/HT in quantitative and increases linearly with surface Au
the absence of any soluble base. This largely reflects the ability concentration/conversion, as anticipated for
a structureꢀ
of gold to ameliorate the strong requirement for additional insensitive reaction in which the reactant coverage is low (weak
NaOH to drive the two aldehyde oxidation steps 1 and 3 adsorption or rapid reaction).
(HMF
→
HMFCA and FFCA
→
FDCA respectively); NaOH
Further evidence that strong HMF adsorption siteꢀblocks
rateꢀenhancements for HMF oxidation fall threeꢀfold as the oxidation of its reactivelyꢀformed products is apparent in Fig. 5
bulk Au content rises from 0.5ꢀ10 wt%, while the sensitivity of
the final FFCA oxidation to NaOH falls 40ꢀfold over the same
gold range. High FDCA yields are therefore achievable either
by using low concentrations of Au in conjunction with a strong
soluble base, or high concentrations of Au on a moderate
strength solid base.
100
90
80
70
60
50
40
30
20
10
0
300
250
200
150
100
50
50 mg
-ve order
in HMF
25 mg
40
0
20
HMF:surface Au
HMF→FDCA
0
20
40
60
80
100
Conversion / %
Fig. 5 (main) Disparate evolution of FDCA yield as a function of either HMF or
HMFCA conversion over 25 mg )0.5 wt%, ) 1 wt%, ) 2 wt%,
5 wt%, and ) 10 wt% Au/HT catalysts, and 50 mg 2 wt% Au/HT; (inset)
normalised FDCA productivity per Au atom as a function of HMF:surface Au
ꢀ
(
ꢀ
(
ꢀ
ꢀ
(
ꢁ(ꢁ)
ꢁ(ꢁ
molar ratio for
concentrations.
2 wt% Au/HT highlighting self-poisoning by high HMF
Fig. 4 (main) Impact of Au loading on the sensitivity of individual oxidation steps
towards soluble base addition over Au/HT catalysts; (inset) Au loading
dependent product selectivity in HMF oxidation in the absence of soluble base.
inset wherein the HMF:surface Au ratio was varied for the 2
wt% Au/HT catalyst. In the absence of diffusion limitations,
and the presence of available reaction sites, the mass
normalized FDCA productivity should be independent of
substrate:catalyst ratio, whereas Fig. 5 inset reveals that halving
the HMF:surface Au ratio imparts a sevenꢀfold increase in
FDCA productivity. Reactive gold sites for HMFCA oxidation
only become available for HMF:surface Au ratios below a
critical threshold wherein it can effectively compete with
adsorption of the parent HMF.
We attribute the loading dependence of these two catalytic
regimes (soluble base
≤ 2 wt% Au > solid base) to competitive
adsorption between HMF and HMFCA. The HMF:surface Au
molar ratio approaches 60:1 for the 0.5 wt% Au/HT catalyst,
hence it is unlikely that the low concentration of geminal diol
formed without NaOH can effectively compete for adsorption
sites over gold nanoparticles. NaOH addition accelerates
geminal diol formation from HMF in solution, displacing the
HMF adsorption equilibrium and liberating reactive gold
surface site for both geminal diol dehydrogenation to HMFCA,
and subsequent OHꢀ mediated oxidative dehydrogenation of
In conclusion, the combination of operando XAS and
detailed kinetic mapping has elucidated the nature of the active
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site and mechanism of Au catalysed 5ꢀHMF aerobic selox to 16. C. Chatterjee, F. Pong and A. Sen, Green Chemistry, 2015, 17, 40ꢀ71.
2,5ꢀFDCA. A delicate balance is revealed between the rate of 17. H. B. Zhao, J. E. Holladay, H. Brown and Z. C. Zhang, Science
base catalysed 5ꢀHMF activation and the latter´s selfꢀpoisoning 2007, 316, 1597ꢀ1600.
of requisite metallic gold sites for subsequent oxidation of 18. M. Moliner, Y. RomanꢀLeshkov and M. E. Davis, Proc. Natl. Acad.
reactivelyꢀformed HMFCA/FFCA intermediates. Hydrotalcite Sci. U. S. A., 2010, 107, 6164ꢀ6168.
solid base can only drive 5ꢀHMF selox in concert with high 19. A. Osatiashtiani, A. F. Lee, D. R. Brown, J. A. Melero, G. Morales
,
concentrations of surface gold, a discovery that has important
implications for gold catalysis and cascade oxidations.
and K. Wilson, Catalysis Science & Technology, 2014, 4, 333ꢀ
342.
20. A. A. Rosatella, S. P. Simeonov, R. F. M. Frade and C. A. M.
Afonso, Green Chemistry, 2011, 13, 754ꢀ793.
Acknowledgements
21. W. Partenheimer and Vladimir V. Grushin, Advanced Synthesis &
Catalysis, 2001, 343, 102ꢀ111.
We thank the EPSRC (EP/G007594/4) for financial support, a
Leadership Fellowship (AFL) and studentship support (LA), the
Royal Society for an Industry Fellowship (KW), and Diamond
Light Source for a beamtime award (SP8688).
22. T. Pasini, M. Piccinini, M. Blosi, R. Bonelli, S. Albonetti, N.
Dimitratos, J. A. LopezꢀSanchez, M. Sankar, Q. He, C. J.
Kiely, G. J. Hutchings and F. Cavani, Green Chemistry, 13,
2091ꢀ2099.
23. Z. Miao, Y. Zhang, X. Pan, T. Wu, B. Zhang, J. Li, T. Yi, Z. Zhang
Notes and references
European Bioenergy Research Institute, Aston University, Birmingham
and X. Yang, Catalysis Science & Technology, 2015, 5, 1314ꢀ
a
1322.
B4 7ET, UK.
24. N. Zheng and G. D. Stucky, Chemical Communications, 2007, 3862ꢀ
3864.
b
Diamond Light Source, Harwell Science and Innovation Campus,
Didcot OX11 0DE, UK.
25. C. Della Pina, E. Falletta, L. Prati and M. Rossi, Chemical Society
Reviews, 2008, 37, 2077ꢀ2095.
†
Electronic Supplementary Information (ESI) available: Catalyst
synthesis, additional characterisation and reaction conditions. See
DOI: 10.1039/b000000x/
26. L. Prati and M. Rossi, Journal of Catalysis, 1998, 176, 552ꢀ560.
27. X. Wan, C. Zhou, J. Chen, W. Deng, Q. Zhang, Y. Yang and Y.
Wang, ACS Catalysis, 2014, 4, 2175ꢀ2185.
1. N. Armaroli and V. Balzani, Angew. Chem.ꢀInt. Edit., 2007, 46, 52ꢀ
66.
28. B. F. Sels, D. E. De Vos and P. A. Jacobs, Catal. Rev.ꢀSci. Eng.
2001, 43, 443ꢀ488.
,
2. G.ꢀQ. Chen and M. K. Patel, Chemical Reviews, 2011, 112, 2082ꢀ
2099.
29. Y. Ono, Journal of Catalysis, 2003, 216, 406ꢀ415.
30. A. Takagaki, S. Nishimura and K. Ebitani, in Heterogeneous
Catalysts for Clean Technology, WileyꢀVCH Verlag GmbH &
Co. KGaA, 2013, pp. 125ꢀ171.
3. P. Azadi, O. R. Inderwildi, R. Farnood and D. A. King, Renewable
and Sustainable Energy Reviews, 2013, 21, 506ꢀ523.
4. J. J. Bozell and G. R. Petersen, Green Chemistry, 2010, 12, 539ꢀ554.
5. B. Kamm and M. Kamm, Chemie Ingenieur Technik, 2007, 79, 592ꢀ
603.
31. N. K. Gupta, S. Nishimura, A. Takagaki and K. Ebitani, Green
Chemistry, 13, 824ꢀ827.
32. G. Yi, S. P. Teong, X. Li and Y. Zhang, ChemSusChem, 2014, 7,
6. Y. Y. Gorbanev, S. K. Klitgaard, J. M. Woodley, C. H. Christensen
2131ꢀ2135.
and A. Riisager, ChemSusChem, 2009, 2, 672ꢀ675.
33. W. Fang, J. Chen, Q. Zhang, W. Deng and Y. Wang, Chemistry – A
European Journal, 2011, 17, 1247ꢀ1256.
7. O. Casanova, S. Iborra and A. Corma, ChemSusChem, 2009, 2, 1138ꢀ
1144.
34. S. Klitgaard, A. DeLa Riva, S. Helveg, R. Werchmeister and C.
Christensen, Catal Lett, 2008, 126, 213ꢀ217.
8. S. E. Davis, L. R. Houk, E. C. Tamargo, A. K. Datye and R. J. Davis,
Catalysis Today 160, 55ꢀ60.
,
35. L. Prati, P. Spontoni and A. Gaiassi, Top Catal, 2009, 52, 288ꢀ296.
36. A. Villa, G. M. Veith and L. Prati, Angewandte Chemie International
Edition, 2010, 49, 4499ꢀ4502.
9. S. E. Davis, M. S. Ide and R. J. Davis, Green Chemistry, 2013, 15
,
17ꢀ45.
10. R.ꢀJ. van Putten, J. C. van der Waal, E. de Jong, C. B. Rasrendra, H.
37. B. N. Zope, D. D. Hibbitts, M. Neurock and R. J. Davis, Science
2010, 330, 74ꢀ78.
,
J. Heeres and J. G. de Vries, Chemical Reviews, 2013, 113
,
1499ꢀ1597.
38. T. Balcha, J. R. Strobl, C. Fowler, P. Dash and R. W. J. Scott, ACS
Catalysis, 2011, , 425ꢀ436.
11. A. Corma, S. Iborra and A. Velty, Chemical Reviews, 2007, 107
,
1
2411ꢀ2502.
39. C. D. Pina, E. Falletta and M. Rossi, Chemical Society Reviews
2012, 41, 350ꢀ369.
,
12. M. Stöcker, Angewandte Chemie International Edition, 2008, 47
,
9200ꢀ9211.
40. J. L. Shumaker, C. Crofcheck, S. A. Tackett, E. SantillanꢀJimenez
and M. Crocker, Catal Lett, 2007, 115, 56ꢀ61.
13. P. N. R. Vennestrøm, C. M. Osmundsen, C. H. Christensen and E.
Taarning, Angewandte Chemie International Edition, 2011, 50
,
41. J. M. Fraile, N. Garcia, J. A. Mayoral, E. Pires and L. Roldan, Appl.
Catal. AꢀGen., 2009, 364, 87ꢀ94.
10502ꢀ10509.
14. R. A. Sheldon, Green Chemistry, 2014, 16, 950ꢀ963.
15. P. Ferrini and R. Rinaldi, Angewandte Chemie International Edition
2014, 53, 8634ꢀ8639.
42. H. E. Cross and D. R. Brown, Catal. Commun., 2010, 12, 243ꢀ245.
43. D. G. Cantrell, L. J. Gillie, A. F. Lee and K. Wilson, Applied
Catalysis A: General, 2005, 287, 183ꢀ190.
,
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 5

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44. A. Hugon, N. E. Kolli and C. Louis, Journal of Catalysis, 2010, 274
,
,
239ꢀ250.
45. R. Zanella, L. Delannoy and C. Louis, Applied Catalysis A: General
2005, 291, 62ꢀ72.
46. D. Glasner and A. I. Frenkel, AIP Conference Proceedings, 2007,
882, 746ꢀ748.
47. A. I. Frenkel, A. Yevick, C. Cooper and R. Vasic, in Annual Review
of Analytical Chemistry, Vol 4, eds. R. G. Cooks and E. S.
Yeung, Annual Reviews, Palo Alto, 2011, vol. 4, pp. 23ꢀ39.
48. S. Biella, L. Prati and M. Rossi, Journal of Molecular Catalysis A:
Chemical, 2003, 197, 207ꢀ212.
49. S. E. Davis, B. N. Zope and R. J. Davis, Green Chemistry, 14, 143ꢀ
147.
50. S. Subbiah, S. P. Simeonov, J. M. S. S. Esperanca, L. P. N. Rebelo
and C. A. M. Afonso, Green Chemistry, 2013, 15, 2849ꢀ2853.
51. C. Shang and Z.ꢀP. Liu, Journal of the American Chemical Society
2011, 133, 9938ꢀ9947.
,
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