Dean Howard Barrett

Physical and chemical studies of tungsten carbide catalysts: effects of Ni promotion and sulphonated carbon

Ni promoted tungsten carbides have been shown to be an effective catalyst for cellulose conversion reaction. With the use of both in situ and ex situ techniques an investigation into the physical and chemical aspects of the Ni-promoted tungsten carbide catalyst supported on activated carbon either in pure form or functionalized with sulfuric acid was conducted. In situ XRD analysis performed during the carburization process showed that non-promoted samples formed a mixture of nanosized W2C, WC1−x and WC carbide phases. In the case of Ni promoted catalysts, in situ XRD, XANES, XPS and TEM analysis revealed that Ni aids in lowering the carburization temperature by 50 °C but also assisted in the deposition of polymeric carbon onto the catalyst surface which reduced cellulose conversion. However, the results indicate beneficial effects caused by the high carbon coverage by stopping the W2C to WC carbide phase transition. Thus, carburization of Ni promoted samples produced only W2C phase, which is stable up to 800 °C. The functionalization of activated-carbon with –SO3H not only increases the hydrolysis of cellulose but also lead to a greater dispersion of Ni over the catalyst. The resulting improvement in the interaction between Ni/W/C increases the cellulose transformation in a one-pot synthesis towards the production of ethylene glycol.

X-ray powder diffraction at the XRD1 beamline at LNLS

Various upgrades have been completed at the XRD1 beamline at the Brazilian synchrotron light source (LNLS). The upgrades are comprehensive, with changes to both hardware and software, now allowing users of the beamline to conduct X-ray powder diffraction experiments with faster data acquisition times and improved quality. The main beamline parameters and the results obtained for different standards are presented, showing the beamline ability of performing high-quality experiments in transmission geometry. XRD1 operates in the 5.5-14 keV range and has a photon flux of 7.8 × 109 photons s-1 (with 100 mA) at 12 keV, which is one of the typical working energies. At 8 keV (the other typical working energy) the photon flux at the sample position is 3.4 × 1010 photons s-1 and the energy resolution ΔE/E = 3 × 10-4.

Promotion effects of Pd on tungsten carbide catalysts: physiochemical properties and cellulose conversion performance

A multi-functional catalyst, which is able to perform both retro-aldol reactions followed by hydrogenation, is required to convert cellulose into value-added ethylene glycol (EG) in a one-pot reaction. Herein, we show the results of a catalyst comprising Pd-promoted tungsten carbide supported on activated carbon. Pd acts to hinder carbon deposition onto the catalyst surface during the carburization process, through the inhibition of methane decomposition species on the catalyst surface. XPS and TEM analysis show a cleaner surface which improves the W/C ratio. The enhanced interaction between Pd and W2C, results in higher cellulose conversions, and higher ethylene glycol (EG) yields when compared to non-promoted or Ni promoted tungsten carbide catalysts reported elsewhere. XAS, HR-TEM and SI-XEDS analysis showed Pd nanoparticles are well dispersed on the surface and in contact with W2C. Despite higher carburization temperatures, Pd-promoted tungsten carbide catalysts enhance the catalytic properties of the one-pot cellulose conversion reaction towards EG production when compared to Ni-promoted catalysts under the same catalytic reaction conditions.

Hybrid Organic-Inorganic Anatase as a Bifunctional Catalyst for Enhanced Production of 5-Hydroxymethylfurfural from Glucose in Water

Hybrid organic-inorganic anatase (hybrid-TiO2 ) is prepared by a facile hydrothermal synthesis method employing citric acid. The synthetic approach results in a high surface-area nanocrystalline anatase polymorph of TiO2 . The uncalcined hybrid-TiO2 is directly studied as a catalyst for the conversion of glucose into 5-hydroxymethylfurfural (HMF). In the presence of the hybrid-TiO2 , HMF yields up to 45 % at glucose conversions up to 75 % were achieved in water at 130 °C in a monophasic batch reactor. As identified by Ti K-edge XANES, hybrid-TiO2 contains a large fraction of fivefold coordinatively unsaturated TiIV sites, which act as the Lewis acid catalyst for the conversion of glucose into fructose. As citric acid is anchored in the structure of hybrid-TiO2 , carboxylate groups seem to catalyze the sequential conversion of fructose into HMF. The fate of citric acid bound to anatase and the TiIV Lewis acid sites throughout recycling experiments is also investigated. In a broader context, this contribution outlines the importance of hydrothermal synthesis for the creation of water-resistant Lewis acid sites for the conversion of sugars. Importantly, the use of the hybrid-TiO2 with no calcination step contributes to dramatically decreasing the energy consumption in the catalyst preparation.

SÍNTESE E CARACTERIZAÇÃO DE CATALISADORES DE Ni SUPORTADOS EM Nb2O5 PARA CONVERSÃO DE CELULOSE

Resumo A conversão catalítica da celulose em biocombustíveis e produtos químicos é uma das rotas mais promissoras para a viabilidade econômica das biorrefinarias. O trabalho fundamenta-se na síntese de catalisadores de níquel suportados em Nb2O5, visando investigar a influência de parâmetros de síntese nas propriedades físicas, químicas e morfológicas do catalisador para ser ativo na reação de conversão da celulose.

Variable Temperature Study of Au and Au-Pt Nanoparticles on Selected Oxide Supports

We report on the size relationship of Au and Au-Pt nanoparticles that were synthesised on silica and anatase phase titania supports. Deposition-precipitation (DP) of metal chlorides with the addition of urea and ammonium hydroxide was used to produce the nanoparticles. The relative particle size relationship of the Au and Au-Pt nano particles (NPs) was investigated, relating the Pt concentration and the support polymorph over a temperature range. It was found, with the use of in-situ variable temperature powder X-ray diffraction (VT-PXRD) and transmission electron microscopy (TEM), that the addition of Pt to the Au system corresponded to a reduction in particle size over a broad temperature range.