Olusola O. James

Towards the conversion of carbohydrate biomass feedstocks to biofuels via hydroxylmethylfurfural

This review appraises the chemical conversion processes recently reported for the production of hydroxylmethylfurfural (HMF), a key biorefining intermediate, from carbohydrate biomass feedstocks. Catalytic sites or groups required for the efficient and selective conversion of hexose substrates to HMF are examined. The principle of concerted catalysis was used to rationalise the dehydration of fructose and glucose to HMF in non-aqueous media. A survey of reported reaction routes to diesel-range biofuel intermediates from HMF or furfural is presented and self-condensation reaction routes for linking two or more HMF and furfural units together toward obtaining kerosene and diesel-range biofuel intermediates are highlighted. The reaction routes include: benzoin condensation, condensation of furfuryl alcohols, hetero Diels–Alder reaction and ketonisation reaction. These reaction routes are yet to be exploited despite their potential for obtaining kerosene and diesel-range biofuel intermediates exclusively from furfural or hydroxylmethylfurfural.

Reflections on the chemistry of the Fischer–Tropsch synthesis

Fischer–Tropsch synthesis (FTS) occupies a key position in the search for alternatives to petroleum for obtaining liquid hydrocarbons. Hydrocarbons can be produced from alternative carbonaceous resources (natural gas, coal, biomass and waste) through FTS and the use of biomass is particularly attractive from a carbon footprint point of view. However, the nature of biomass resources dictates a different exploration approach compared to fossil fuel resources. Compared to coal and natural gas based FTS processes where economics of scale is an advantage, a Biomass-to-Liquid (BTL) plant is more suited for smaller scale operation. Thus, the BTL process economy will benefit from a condensed FTS processes. Moreover, considering the expected role of FTS in regional and global hydrocarbon supply in the near future, it becomes pertinent to strive towards improving the process economy. This requires molecular and process engineering and detailed knowledge of the reaction is a pre-requisite to engineering the reaction at molecular level. Syngas to hydrocarbon involves consecutive steps of CO activation, C–C coupling, hydrogenation and desorption of the hydrocarbon product. Atomic details of the dynamics of these steps are still unclear. Recently, clearer pictures about activation are now available. However, over the course of ninety years since the first report on an FTS, proposed pathway of C–C coupling has come full cycle from oxygenate to nonoxygenate and back to oxygenate intermediates. To this end, we attempted an X-ray of progress made at providing answers to issues in the chemistry of FTS. The review focuses on product distribution, macro kinetics and the mechanism of FTS. We compare FTS with other C–C coupling reactions of CO, identify catalytic entities for controlling product selectivity and finally we offer an outlook on future directions of fundamental research towards resolving the lingering questions on the mechanism of C–C coupling in FTS.

Barium, calcium and magnesium doped mesoporous ceria supported gold nanoparticle for benzyl alcohol oxidation using molecular O2

In the era of sustainable energy, catalysis using gold nanoparticles has drawn considerable attention from world researchers. Oxidation of benzyl alcohol by molecular O2 is an atom efficient path to synthesize benzaldehyde. Nanocrystalline ceria has been proven as a useful support to disperse gold nanoparticles since last few years, however there are a few reports on mesoporous ceria supported gold nanoparticles. In this work a systematic investigation was carried out to improve the activity of Au/CeO2 catalyst by incorporating Ba2+, Ca2+ and Mg2+ cations into the ceria lattice through a sol–gel procedure. Both the doped ceria and ceria supported gold nanoparticles are characterized by BET S.A, XRD, TEM, SAXS, XPS, TPR, CO2-TPD techniques. BET S.A measurements show the mesoporous oxides where H3 hysteresis loops are found. The decrease in the crystallite size of ceria after doping by metal cations is observed in the XRD measurement. The TEM and HRTEM characterization shows the nanocrystalline particle size around 30–50 nm and gold nanoparticles around 10–15 nm in size. Distribution in the particle size for doped ceria have been obtained using SAXS measurements where narrow distributions of ceria particles are found in the 10–20 nm range. The existence of oxide vacancies and the mixture of Ce3+/Ce4+ oxidation states are observed for doped ceria materials in the XPS investigation. The strong gold-support interaction was also evidenced by XPS characterization where oxidic gold was found on the doped ceria surface. Lowering of the reduction peak in ceria after gold nanoparticle deposition was observed from TPR investigation whereas the change in basic site distribution is observed from CO2 TPD experiment, instigating new insights into the surface properties of the catalysts. The catalytic activities of the catalysts were determined for benzyl alcohol oxidation reactions using molecular O2. The catalytic activity was in the order of Au/Ba–CeO2 > Au/Ca–CeO2 > Au/Mg–CeO2 > Au/CeO2. The synergistic effect of gold nanoparticles and dopant cations to the ceria was explained in this work.

TPR and TPD studies of effects of Cu and Ca promotion on Fe–Zn-based Fischer–Tropsch catalysts

AbstractTemperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) were used to study the effects of Cu and Ca promotion on Fe–Zn-based Fischer–Tropsch catalysts. The reduction temperature for Fe2O3 → Fe3O4 was unaffected by Ca addition but decreased when promoted with Cu. Fe–Zn promoted with Cu and Ca showed even much lower reduction temperature for Fe2O3 → Fe3O4. Ca promotion enhances carburization and increases surface acidity and basicity of the Fe–Zn oxide precursor. While Cu inhibits carburization and decreases the surface acidity and basicity of the Fe–Zn oxide precursor. The implications of these effects on the application of catalysts for FT are discussed. Graphical AbstractThe α-chymostrypsin hydrolysis of PNPA in AOT/isooctane/ buffer RMs has been studied with varying water content, w0, in the presence of Triton-X 100 and sulfobetaine surfactants. The activity of α-CT depends on the water pool size and the amount of AOT and mixed surfactant media.