Aqueous-phase reforming of alcohols with three carbon atoms on carbon-supported Pt

MOF-based heterogeneous catalysis in continuous flow via incorporation onto polymer-based spherical activated carbon supports

We present an approach to harnessing the tuneable catalytic properties of complex nanomaterials for continuous flow heterogeneous catalysis by combining them with the scalable and industrially implementable properties of carbon pelleted supports. This approach, in turn, will enable these catalytic materials, which largely currently exist in forms unsuitable for this application (e.g. powders), to be fully integrated into large scale, chemical processes. A composite heterogeneous catalyst consisting of a metal-organic framework-based Lewis acid, MIL-100(Sc), immobilised onto polymer-based spherical activated carbon (PBSAC) support has been developed. The material was characterised by focused ion beam-scanning electron microscopy-energy dispersive X-ray analysis, powder X-ray diffraction, N2 adsorption, thermogravimetric analysis, atomic absorption spectroscopy, light scattering and crush testing with the catalytic activity studied in continuous flow. The mechanically robust spherical geometry makes the composite material ideal for application in packed-bed reactors. The catalyst was observed to operate without any loss in activity at steady state for 9 hours when utilised as a Lewis acid catalyst for the intramolecular cyclisation of (±)-citronellal as a model reaction. This work paves the way for further development into the exploitation of MOF-based continuous flow heterogeneous catalysis.

Hydrogen production via aqueous-phase reforming for high-temperature proton exchange membrane fuel cells - a review

Aqueous-phase reforming (APR) can convert methanol and other oxygenated hydrocarbons to hydrogen and carbon dioxide at lower temperatures when compared with the corresponding gas phase process. APR favours the water-gas shift (WGS) reaction and inhibits alkane formation; moreover, it is a simpler and more energy efficient process compared to gas-phase steam reforming. For example, Pt-based catalysts supported on alumina are typically selected for methanol APR, due to their high activity at temperatures of circa 200°C. However, non-noble catalysts such as nickel (Ni) supported on metal-oxides or zeolites are being investigated with promising results in terms of catalytic activity and stability. The development of APR kinetic models and reactor designs is also being addressed to make APR a more attractive process for producing in situ hydrogen. This can also lead to the possibility of APR integration with high-temperature proton exchange membrane fuel cells. The integration can result into increased overall system efficiency and avoiding critical issues faced in the state-of-the-art fuel cells integrated with methanol steam reforming.

Aqueous phase reforming of birch and pine hemicellulose hydrolysates

The current work focuses on studying the aqueous phase reforming (APR) of pine and birch hydrolysate obtained from waste wood by using organic acids available from biorefineries. Processing of representative synthetic mixtures was utilized in the work in order to support data interpretation related to the influence of different chemical compound and processing parameters on the APR of the actual hydrolysates. It was shown, that hydrogenation of the hydrolysates prior to APR was not feasible in the presence of formic acid, which ruled out one potential processing route. However, it was successfully demonstrated that birch and pine hydrolysates could be directly processed obtaining close to full conversion. The best results were obtained with tailored bimetallic Pd-Pt/sibunit catalyst in a trickle bed reactor system in the temperature range 175 °C-225 °C.

Continuous aqueous phase reforming of a synthetic brewery wastewater with Pt/C and PtRe/C catalysts for biohydrogen production

This work investigates H₂ production through aqueous phase reforming (APR) of synthetic brewery wastewater in a continuous fixed bed reactor with Pt and PtRe (3 wt %) catalysts supported on activated carbon. The influence of weight hourly space velocity (WHSV) and superficial Ar gas flow velocity (V_Ar) was assessed for the sake of optimisation, while reaction temperature and pressure were maintained at 225 °C and 28 bar, respectively. H₂ production was found to be higher using the PtRe catalyst at the lowest WHSV (0.03 h^-1) and highest V_Ar (0.8 cm s^-1). The comparison of the maximum H₂ production obtained in this work (27.9 μmol min^-1) with other treatment processes shows the potential of the application of APR process for H₂ production from brewery wastewater. Despite the different reaction conditions tested, the catalysts showed deactivation with time on stream, which was related to the formation of solid deposits on the surface of the catalysts. Therefore, future research should be related to the development of more stable catalysts, strategies that avoid deactivation by coking and regeneration processes.

Citric acid modified Ni3P as a catalyst for aqueous phase reforming and hydrogenolysis of glycerol to 1,2-PDO

The addition of citric acid reduced the Ni3P particle size, leading to high performance in glycerol hydrogenolysis without external H2.

Influence of the Catalyst Particle Size on the Aqueous Phase Reforming of n-Butanol Over Rh/ZrO2

Butanol is a by-product obtained from biomass that can be valorized through aqueous phase reforming. Rh/ZrO₂ catalysts were prepared and characterized, varying the size of the support particles. The results showed a relatively mild effect of internal mass transport on butanol conversion. However, the influence of internal transport limitations on the product distribution was much stronger, promoting consecutive reactions, i.e., dehydrogenation, hydrogenolysis, and reforming of propane and ethane. Hydrogen consuming reactions, i.e., hydrogenolysis, were more strongly enhanced than hydrogen producing reactions due to internal concentration gradients. Large support particles deactivated faster, attributed to high concentrations of butyraldehyde inside the catalyst particles, enhancing deposit formation via aldol condensation reactions. Consequently, also the local butyric acid concentration was high, decreasing the local pH, enhancing Rh leaching. The influence of internal transfer limitation on product distribution and stability is discussed based on a reaction scheme with three main stages, i.e., (1) formation of liquid intermediates via dehydrogenation, (2) formation of gas via decarbonylation/decarboxylation reactions, and (3) hydrocarbon hydrogenolysis/reforming/dehydrogenation.

Aqueous phase reforming of xylitol and xylose in the presence of formic acid

Aqueous phase reforming (APR) of xylose and xylitol was studied over Pt/Pd catalysts in the presence of formic acid simulating an industrial feedstock.

The influence of hydroxy groups on the adsorption of three-carbon alcohols on Ni(111), Pd(111) and Pt(111) surfaces: a density functional theory study within the D3 dispersion correction

Experimentally, steric and inductive effects have been suggested as key parameters in the adsorption and reactivity of alcohols on transition-metal (TM) surfaces, however, our atomistic understanding of the behavior of alcohols in catalysis is far from satisfactory, in particular, due to the role of hydroxy groups in the adsorption properties of C3 alcohols on TM surfaces. In this study, we investigated those effects through ab initio calculations based on density functional theory employing a semilocal exchange-correlation functional within van der Waals corrections (the D3 framework) for the adsorption of C3 alcohols with different numbers and positions of OH groups, namely, propane, 1-propanol, 2-propanol, 1,2-propanediol, 1,3-propanediol and glycerol, on the compact Ni(111), Pd(111) and Pt(111) surfaces. As expected, we found that the adsorption energy is affected by the number of hydroxy groups with similar values for each pair of regioisomers, which clearly indicates the effect of the number of OH groups. Based on Bader charge analysis, we found an effective charge transfer from the C3 molecules to the substrates, which can explain the reduction in the work function due to adsorption. Upon adsorption, the alpha carbon to the OH group closest to the surface and the central carbon are the most positively charged atoms, which increases the lability of their bonded H atoms. In addition, the depletion of electron density between the C-H and O-H bonds closer to the surfaces corroborated their stretching, suggesting that the proximity of the adsorbates to the surfaces affects the acidity of these H atoms, as well as inductive effects within the molecules.

Sibunit-Supported Mono- and Bimetallic Catalysts Used in Aqueous-Phase Reforming of Xylitol

Carbon-supported mono- and bimetallic catalysts prepared via incipient wetness impregnation were systematically studied in aqueous-phase reforming (APR) of xylitol aiming at hydrogen production from biomass. The catalytic performance of several VIII group metals and their combinations, such as Pt, Ni, Pt–Ni, Re, Pt–Re, Ru, Pt–Ru, and Pt–Co, was compared for xylitol APR in a fixed-bed reactor at 225 °C and 29.7 bar (N₂). Ni/C, Ru/C, and Re/C catalysts displayed significantly lower activity compared to others. Activity and selectivity to H₂ of bimetallic Pt–Ni/C, Pt–Co/C, and Pt–Ru/C catalysts were close to that of Pt/C. Pt–Re/C catalyst showed an outstanding performance which was accompanied by a shift of the reaction pathways to the alkane formation and thereby lower hydrogen selectivity. Addition of the second metal to Pt was not found to be beneficial for hydrogen production, thus leaving Pt/C as the optimum carbon-supported catalyst.