Andrew R. Tadd

Hydroformylation of 1-hexene in supercritical carbon dioxide using a heterogeneous rhodium catalyst. 3. Evaluation of solvent effects

The heterogeneously catalyzed hydroformylation of 1-hexene in supercritical carbon dioxide is demonstrated as an alternative to homogeneous catalysis through the use of a rhodium–phosphine catalyst tethered to a silica support. Reaction over the heterogeneous catalyst in supercritical CO2 is compared with the use of this catalyst in liquid-phase toluene, and toluene expanded with CO2. Likewise, the performance of the tethered catalyst is compared with a homogeneous rhodium–phosphine catalyst, and shown to be equally effective under identical reaction conditions. Comparable reaction rates were obtained using the heterogeneous rhodium catalyst in supercritical CO2 and CO2-expanded toluene, both of which were superior to the reaction rate with the heterogeneous catalyst in liquid-phase toluene. Initial aldehyde selectivity obtained with the heterogeneous species was also comparable to that obtained with the homogeneous catalyst, but decreased over the course of the reaction. These results demonstrate the value of using phase behavior, and the importance of understanding this behavior in the development and analysis of greener solvent/catalyst systems.

Hydroformylation of 1-hexene in supercritical carbon dioxide using a heterogeneous rhodium catalyst. 1. Effect of process parameters

Abstract The hydroformylation of 1-hexene in supercritical carbon dioxide is catalyzed with a heterogeneous rhodium catalyst that is active, selective, and stable for the formation of heptanal. The aldehyde yield and regioselectivity can be affected through changes in catalyst support structure, CO2 solvent pressure, and reaction temperature. A complex reaction pathway model is described that allows determination of rate constants, which are in turn, evaluated as a function of temperature and pressure. Analysis reveals an activation volume of −474 cm3/mol and activation energy of 31.9 kJ/mol for the hydroformylation pathways.

Catalytic reforming of liquid hydrocarbons for on-board solid oxide fuel cell auxiliary power units

Catalytic reforming of liquid transportation fuels and their hydrocarbon components via steam reforming, catalytic partial oxidation, and autothermal reforming is reviewed. The review focuses on fuel reforming to generate hydrogen-rich syngas for on-board applications, with emphasis on solid-oxide f...

FEEDSTOCK-FLEXIBLE REFORMER SYSTEM (FFRS) FOR SOLID OXIDE FUEL CELL (SOFC)- QUALITY SYNGAS

The U.S. Department of Energy National Energy Technology Laboratory funded this research collaboration effort between NextEnergy and the University of Michigan, who successfully designed, built, and tested a reformer system, which produced highquality syngas for use in SOFC and other applications, and a novel reactor system, which allowed for facile illumination of photocatalysts. Carbon and raw biomass gasification, sulfur tolerance of non-Platinum Group Metals (PGM) based (Ni/CeZrO2) reforming catalysts, photocatalysis reactions based on TiO2, and mild pyrolysis of biomass in ionic liquids (ILs) were investigated at low and medium temperatures (primarily 450 to 850 C) in an attempt to retain some structural value of the starting biomass. Despite a wide range of processes and feedstock composition, a literature survey showed that, gasifier products had narrow variation in composition, a restriction used to develop operating schemes for syngas cleanup. Three distinct reaction conditions were investigated: equilibrium, autothermal reforming of hydrocarbons, and the addition of O2 and steam to match the final (C/H/O) composition. Initial results showed rapid and significant deactivation of Ni/CeZrO2 catalysts upon introduction of thiophene, but both stable and unstable performance in the presence of sulfur were obtained. The key linkage appeared to be the hydrodesulfurization activity of the Ni reforming catalysts. For feed stoichiometries where high H2 production was thermodynamically favored, stable, albeit lower, H2 and CO production were obtained; but lower thermodynamic H2 concentrations resulted in continued catalyst deactivation and eventual poisoning. High H2 levels resulted in thiophene converting to H2S and S surface desorption, leading to stable performance; low H2 levels resulted in unconverted S and loss in H2 and CO production, as well as loss in thiophene conversion. Bimetallic catalysts did not outperform Ni-only catalysts, and small Ni particles were found to have lower activities under S-free conditions, but did show less effect of S on performance, in this study. Imidazolium-based ILs, choline chloride compounds and low-melting eutectics of metal nitrates were evaluated, and it was found that, ILs have some capacity to dissolve cellulose and show thermal stability to temperatures where pyrolysis begins, have no vapor pressure, (simplifying product recoveries), and can dissolve ionic metal salts, allowing for the potential of catalytic reactions on breakdown intermediates. Clear evidence of photoactive commercial TiO2 was obtained, but in-house synthesis of photoactive TiO2 proved difficult, as did fixed-bed gasification, primarily due to the challenge of removing the condensable products from the reaction zone quickly enough to prevent additional reaction. Further investigation into additional non-PGM catalysts and ILs is recommended as a follow-up to this work.