Bifunctional SO4/ZrO2 catalysts for 5-hydroxymethylfufural (5-HMF) production from glucose

The telescopic conversion of glucose to fructose and then 5-hydroxymethylfurfural (5-HMF), the latter a potential, bio-derived platform chemical feedstock, has been explored over a family of bifunctional sulfated zirconia catalysts possessing tuneable acid-base properties. Characterisation by acid-base titration, XPS, XRD and Raman reveal that submonolayer SO4 coverages offer the ideal balance of basic and Lewis-Brønsted acid sites required to respectively isomerise glucose to fructose, and subsequently dehydrate fructose to 5-HMF. A constant acid site normalised turnover frequency is observed for fructose dehydration to 5-HMF, confirming a common Brønsted acid site is responsible for this transformation. This journal is © The Royal Society of Chemistry.

Physicochemical properties of WOx/ZrO2 catalysts for palmitic acid esterification

A series of WOx/ZrO2 with various tungsten loadings was prepared via incipient-wetness impregnation of zirconium hydroxide. The resulting thermally processed materials were characterised by XRD, XPS, porosimetry, NH3-TPD and pyridine FTIR spectroscopy to elucidate their composition, morphology and acidity, and subsequently tested in the esterification of palmitic acid with methanol. Catalytic performance was strongly dependent upon calcination temperature and W surface density. Esterification activity increased with increasing surface W density, reaching a maximum at 8.9Wnm-2 corresponding to near monolayer coverage. Subsequent growth of crystalline WO3 lowered activity, consistent with a decrease in the density of active surface sites. Calcination temperatures as high as 800°C increased surface acidity and hence catalytic activity. The formation of polymeric tungstate species on zirconia is necessary to generate the Brönsted acid sites responsible for palmitic acid esterification under mild conditions. © 2014 Elsevier B.V.

Zr-containing hybrid organic-inorganic mesoporous materials:hydrophobic acid catalysts for biodiesel production

Zirconium-containing periodic mesoporous organosilicas (Zr-PMOs) with varying framework organic content have been synthesized through a direct synthesis method. These materials display the excellent textural properties of the analogous inorganic solid acid Zr-SBA-15 material. However, the substitution of silica by organosilicon species provides a strong hydrophobic character. This substitution leads to meaningful differences in the environment surrounding the zirconium metal sites, leading the modification of the catalytic properties of these materials. Although lower metal incorporation is accomplished in the final materials, leading to a lower population of metal sites, hydrophobisation leads to an impressive beneficial effect on the intrinsic catalytic activity of the zirconium sites in biodiesel production by esterification/transesterification of free fatty acid -containing feedstock. Moreover, the catalytic activity of the highly hybridised materials is hardly affected in presence of large amounts of water, confirming their very good water-tolerance. This makes Zr-PMO materials interesting catalysts for biodiesel production from highly acidic water-containing feedstock. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tuning solid acid catalysts for glucose conversion to platform chemicals

Worldwide concern over dwindling fossil fuel reserves and impact of CO2 emissions on climate change means there is an urgent need to reduce our dependence on oil based sources of fuels and chemicals. The direct conversion of lignocellulosic derived glucose to 5-Hydroxymethylfurfural (5-HMF) is an attractive process for the production of chemicals and fuels but requires a bi-functional catalyst with acid-base or Lewis-Brönsted sites which can operate efficiently in the aqueous phase. While conventionally viewed as a superacid, the potential for tuning the acid strength in SO4/ZrO2 and potential for coupling bi-functional ZrO2-SO4/ZrO2 sites at low sulfate contents have been overlooked. Our previous work has shown effective tuning of the acid strength in SO4/ZrO2 can be used to direct selectivity in terpene isomerisation thus we rationalised control over HMF selectivity could achieved in a similar fashion. Here we report on a systematic study of the impact of acid properties of SO4/ZrO2 catalysts on the conversion of C6 sugars to 5-HMF in aqueous media and correlate the surface acid-base properties with glucose isomerisation and dehydration capabilities.

Heterogeneous catalysts for converting renewable feedstocks to fuels and chemicals

The combination of dwindling oil reserves and growing concerns over carbon dioxide emissions and associated climate change is driving the urgent development of routes to utilise renewable feedstocks as sustainable sources of fuel and chemicals. Catalysis has a rich history of facilitating energy-efficient selective molecular transformations and contributes to 90% of chemical manufacturing processes and to more than 20% of all industrial products. In a post-petroleum era, catalysis will be central to overcoming the engineering and scientific barriers to economically feasible routes to biofuels and chemicals. This chapter will highlight some of the recent developments in heterogeneous catalytic technology for the synthesis of fuels and chemicals from renewable resources, derived from plant and aquatic oil sources as well as lignocellulosic feedstocks. Particular attention will be paid to the challenges faced when developing new catalysts and importance of considering the design of pore architectures and effect of tuning surface polarity to improve catalyst compatibility with highly polar bio-based substrates.

Tunable KIT-6 mesoporous sulfonic acid catalysts for fatty acid esterification

We report the first catalytic application of pore-expanded KIT-6 propylsulfonic acid (PrSO H) silicas, in fatty acid esterification with methanol under mild conditions. As-synthesized PrSO H-KIT-6 exhibits a 40 and 70% enhancement in turnover frequency (TOF) toward propanoic and hexanoic acid esterification, respectively, over a PrSO H-SBA-15 analogue of similar 5 nm pore diameter, reflecting the improved mesopore interconnectivity of KIT-6 over SBA-15. However, pore accessibility becomes rate-limiting in the esterification of longer chain lauric and palmitic acids over both solid acid catalysts. This problem can be overcome via hydrothermal aging protocols which permit expansion of the KIT-6 mesopore to 7 nm, thereby doubling the TOF for lauric and palmitic acid esterification over that achievable with PrSO H-SBA-15. © 2012 American Chemical Society.

Bifunctional organorhodium solid acid catalysts for methanol carbonylation

Robust, bifunctional catalysts comprising Rh(CO)(Xantphos) exchanged phosphotungstic acids of general formulas [Rh(CO)(Xantphos)]+n[H3–nPW12O40]n− have been synthesized over silica supports which exhibit tunable activity and selectivity toward direct vapor phase methanol carbonylation. The optimal Rh:acid ratio = 0.5, with higher rhodium concentrations increasing the selectivity to methyl acetate over dimethyl ether at the expense of lower acidity and poor activity. On-stream deactivation above 200 °C reflects Rh decomplexation and reduction to Rh metal, in conjunction with catalyst dehydration and loss of solid acidity because of undesired methyl acetate hydrolysis, but can be alleviated by water addition and lower temperature operation.

Carbon nanotube-supported metal catalysts for NOx reduction using hydrocarbon reductants. Part 1:catalyst preparation, characterization and NOx reduction characteristics

A dual catalyst system for the Selective Catalytic Reduction of NOx with hydrocarbons (HC-SCR), including distinct low and high temperature formulations, is proposed as a means to abate NOx emissions from diesel engines. Given that satisfactory high temperature HC-SCR catalysts are already available, this work focuses on the development of an improved low temperature formulation. Pt supported on multiwalled carbon nantubes (MWCNTs) was found to exhibit superior NOx reduction activity in comparison with Pt/Al2O3, while the MWCNT support displayed a higher resistance to oxidation than activated carbon. Refluxing the MWCNT support in a 1:1 mixture of H2SO4 and HNO3 prior to the metal deposition step proved to be beneficial for the metal dispersion and the NOx reduction performance of the resulting catalysts. This support effect is ascribed to the increased Brønsted acidity of the acid-treated MWCNTs, which in turn enhances the partial oxidation of the hydrocarbon reductant. Further improvements in the HC-SCR performance of MWCNT-based formulations were achieved using a 3:1 Pt–Rh alloy as the supported phase.

Designing heterogeneous catalysts for biodiesel synthesis

Concerns over dwindling oil reserves, carbon dioxide emissions from fossil fuel sources and associated climate change is driving the urgent need for clean, renewable energy supplies. The conversion of triglycerides to biodiesel via catalytic transesterification remains an energetically efficient and attractive means to generate transportation fuel1. However, current biodiesel manufacturing routes employing soluble alkali based catalysts are very energy inefficient producing copious amounts of contaminated water waste during fuel purification. Technical advances in catalyst and reactor design and introduction of non-food based feedstocks are thus required to ensure that biodiesel remains a key player in the renewable energy sector for the 21st century. This presentation will give an overview of some recent developments in the design of solid acid and base catalysts for biodiesel synthesis. A particular focus will be on the benefits of designing materials with interconnected hierarchical macro-mesoporous networks to enhance mass-transport of viscous plant oils during reaction.

Glycerol valorization:dehydration to acrolein over silica-supported niobia catalysts

The catalytic dehydration of glycerol to acrolein is investigated over silica-supported niobia catalysts in a continuous fixed-bed gas-phase reactor. Various supported niobia catalysts are prepared and characterized using surface analysis and spectroscopic methods (XRD, UV-Vis, XPS, N2 adsorption), as well as with ammonia adsorption microcalorimetry. Good results are obtained with initial glycerol conversions of over 70% and with 50-70% selectivity to acrolein. We investigate the influence of changing the catalyst acid strength by varying the niobia content and catalyst calcination temperature. Glycerol conversion and acrolein selectivity depend on the surface acid strength. Catalyst deactivation by coking is also observed, but simple oxidative treatment in air restores the activity of the catalysts completely. © The Author(s) 2010.

Hierarchical nanoporous solid base catalysts for biofuels

Novel macroporous solid bases have been developed as alternative clean technologies to existing commercial homogeneous catalysts for the production of biodiesel from triglycerides; the latter suffer process disadvantages including complex separation and associated saponification and engine corrosion, and are unsuitable for continuous operation. To this end, tuneable macroporous MgAl hydrotalcites have been prepared by an alkali-free route and characterised by TGA, XRD, SEM and XPS. The macropore architecture improves diffusion of bulky triglyceride molecules to the active base sites, increasing activity. Lamellar and macroporous hydrotalcites will be compared for the transesterification of both model and plant oil feedstocks, and structure-reactivity relations identified.

Hierarchical porous catalysts tailored for biodiesel production

There is a pressing need for sustainable transportation fuels to combat both climate change and dwindling fossil fuel reserves. Biodiesel, synthesised from non-food plant (e.g., Jatropha curcas) or algal crops is one possible solution, but its energy efficient production requires design of new solid catalysts optimized for the bulky triglyceride and fatty acid feedstocks. Here we report on the synthesis of hierarchical macroporous-mesoporous silica and alumina architectures, and their subsequent functionalization by propylsulfonic acid groups or alkaline earth oxides to generate novel solid acid and base catalysts. These materials possess high surface areas and well-defined, interconnected macro-mesopore networks with respective narrow pore size distributions tuneable around 300 nm and 5 nm. Their high conductivity and improved mass transport characteristics enhance activity towards transesterification of bulky tricaprylin and palmitic acid esterification, over mesoporous analogues. This opens the way to the wider application of hierarchical catalysts in biofuel synthesis and biomass conversion.

New solid base catalysts for biodiesel synthesis

The application of heterogeneous catalysts for the manufacture of renewable biodiesel fuels offers an exciting, alternative clean chemical technology to current energy intensive processes employing soluble base catalysts. We recently synthesised tuneable MgO nanocrystals as efficent solid base catalysts for biodiesel synthesis, and have developed a simple X-ray spectroscopic method to quantitatively determine surface basicity, thereby providing a rapid screening tool for predicting the reactivity of new solid base catalysts. Promotion of these MgO nanocrystals through Cs doping dramatically enhances biodiesel production rates due to the formaion of a mixed Cs Mg(CO ) phase. These MgO derived nanocatalysts permit energy efficent, continuous processing of diverse, sustainable oil feedstocks in flow reactors.

Heterogeneous catalysts for biodiesel production

The combination of dwindling oil reserves and growing concerns over carbon dioxide emissions and associated climate change is driving the urgent development of clean, sustainable energy supplies. Biodiesel is non-toxic and biodegradable, with the potential for closed CO2 cycles and thus vastly reduced carbon footprints compared with petroleum fuels. However, current manufacturing routes employing soluble catalysts are very energy inefficient and produce copious amounts of contaminated water waste. This review highlights the significant progress made in recent years towards developing solid acid and base catalysts for biodiesel synthesis. Issues to be addressed in the future are also discussed including the introduction of non-edible oil feedstocks, as well as technical advances in catalyst and reactor design to ensure that biodiesel remains a key player in the renewable energy sector for the 21st century.

Designer catalysts for biodiesel synthesis

The combination of dwindling oil reserves and growing concerns over carbon dioxide emissions and associated climate change is driving the urgent development of clean, sustainable energy supplies. Biodiesel is a non-toxic and biodegradable fuel, with the potential for closed CO2 cycles and thus vastly reduced carbon footprints compared with petroleum. However, current manufacturing routes employing soluble catalysts are very energy inefficient, with their removal necessitating an energy intensive separation to purify biodiesel, which in turn produces copious amounts of contaminated aqueous waste. The introduction of non-food based feedstocks and technical advances in heterogeneous catalyst and reactor design are required to ensure that biodiesel remains a key player in the renewable energy sector for the 21st century. Here we report on the development of tuneable solid acid and bases for biodiesel synthesis, which offer several process advantages by eliminating the quenching step and allowing operation in a continuous reactor. Significant progress has been made towards developing tuneable solid base catalysts for biodiesel synthesis, including Li/CaO [1], Mg-Al hydrotalcites [2] and calcined dolomite [3] which exhibit excellent activity for triglyceride transesterification. However, the effects of solid base strength on catalytic activity in biodiesel synthesis remains poorly understood, hampering material optimisation and commercial exploitation. To improve our understanding of factors influencing solid base catalysts for biodiesel synthesis, we have applied a simple spectroscopic method for the quantitative determination of surface basicity which is independent of adsorption probes. Such measurements reveal how the morphology and basicity of MgO nanocrystals correlate with their biodiesel synthesis activity [4]. While diverse solid acids and bases have been investigated for TAG transesterification, the micro and mesoporous nature of catalyst systems investigated to date are not optimal for the diffusion of bulky and viscous C16-C18 TAGs typical of plant oils. The final part of this presentation will address the benefits of designing porous networks comprising interconnected hierarchical macroporous and mesoporous channels (Figure 1) to enhance mass-transport properties of viscous plant oils during biodiesel synthesis [5]. References: [1] R.S. Watkins, A.F. Lee, K. Wilson, Green Chem., 2004, 6, 335. [2]D.G. Cantrell, L.J. Gillie, A.F. Lee and K. Wilson, Appl. Catal. A, 2005, 287,183. [3] C. Hardacre, A.F. Lee, J.M. Montero, L. Shellard, K.Wilson, Green Chem., 2008, 10, 654. [4] J.M. Montero, P.L. Gai, K. Wilson, A.F. Lee, Green Chem., 2009, 11, 265. [5] J. Dhainaut, J.-P. Dacquin, A.F. Lee, K. Wilson, Green Chem., 2010, 12, 296.