| Environmental, economic, political, and social concerns have motivated the search for sustainable energy and chemical sources. While a number of sustainable resources (wind, solar, etc.) can be utilized for energy generation, biomass is the only sustainable resource that has the organic building blocks necessary to produce an array of chemicals. Heterogeneous catalysis offers one technological pathway for the transformation of biomass material into those chemicals. This dissertation focuses on the in-situ spectroscopic characterization of heterogeneous catalysts operating under aqueous phase biomass processing conditions as well as the Au-catalyzed aqueous-phase oxidation of CO and glycerol. Glycerol is a by-product of biodiesel production and its chemical structure is similar to that of carbohydrates found in the majority of plant mass.; In-situ X-ray absorption spectroscopy (XAS) was used to characterize the size of Ru metal particles on various catalyst supports under aqueous conditions typical of biomass conversion. The catalysts, Ru/gamma-A1 2O3, Ru/C, Ru/TiO2, and Ru/SiO2, were evaluated at 473 K, 40 atm H2, in neutral and alkaline aqueous solutions. Upon aqueous treatment significant metal growth was observed for the Ru/gamma-Al2O3 and Ru/SiO2 samples, while the Ru/C and Ru/TiO2 remained quite stable. Post-treatment characterization of the catalyst supports indicated major structural changes of the alumina and silica, which is suggested as the cause of metal particle growth.; The aqueous-phase oxidation of CO was measured over Au catalysts to probe the promotional effect of hydroxyl ions. A carbon-supported Au catalyst that was inactive for vapor-phase CO oxidation resulted in a turnover frequency (TOF) of 5 s-1 operating in 1 M NaOH at 300 K. The TOF for the Au/C catalyst was a strong function of hydroxyl concentration, decreasing by about a factor of 50 when the pH was decreased from 14 to 0.3. Evidently, a catalytic oxidation route that was not available in the vapor phase is enabled by operation in liquid water at high pH. Hydrogen peroxide is also produced during CO oxidation over Au in liquid water, with its formation rate increasing with increased hydroxyl concentration.; The aqueous-phase oxidation of glycerol (10 atm O2, 308--333 K) was performed in a semi-batch reactor over the same Au/C catalyst. High pH was required for catalysis to occur, with the initial TOF increasing with increasing hydroxyl concentration. A TOF of 17 s-1 was obtained over Au/C at 333 K. Similar to CO oxidation in liquid water, H 2O2 is produced during glycerol oxidation at high pH. The formation of the C-C cleavage product glycolic acid is attributed to the peroxide formed during reaction.; Carbon-supported Au particles ranging from 5 to 42 nm as well as unsupported Au powder were evaluated as catalysts in the aqueous-phase oxidation of CO and glycerol to investigate the influence of gold particle size. For the aqueous-phase oxidation of CO (pH = 14, 300 K) the TOF for the 5 nm Au particles was 5 s -1 whereas the TOF for large supported Au (42 nm) and bulk Au were only 0.5 and 0.4 s-1, respectively. The observed rate of peroxide formation during CO oxidation was also much higher on the small Au particles. Oxidation of glycerol in the aqueous phase at 333 K and elevated pH over the same catalysts revealed a similar influence of particle size, with 5 nm Au particles giving a TOF of 17 s-1 whereas larger particles and bulk Au were nearly an order of magnitude less active. However, large Au particles (> 20 nm) were more selective to glyceric acid. The lower selectivity of small Au particles is attributed to a higher formation rate of H2O2 during glycerol oxidation since peroxide affects C-C cleavage reaction.; Carbon-supported AuPd bimetallic catalysts were also prepared, characterized, and evaluated for the aqueous-phase selective oxidation of glycerol. Measurement of the glycerol oxidation TOF (10 atm O2, 333 K) for monometallic Au and Pd... |
