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We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites were converted to oxidic sites. Water aging also induced changes to the non-carbidic carbon deposited during carbide synthesis and increased surface roughness, which in turn affected carbide pore volume and surface area. The extent of these structural changes was sensitive to the initial carbide structure and was lower under actual hydroprocessing conditions indicating the possibility of further improving the hydrothermal stability of Mo carbides by optimizing catalyst structure and operating conditions. Mo carbides were active in acetic acid conversion in the presence of liquid water, their activity being comparable to that of Ru/C. The results suggest that effective and inexpensive bio-oil hydroprocessing catalysts could be designed based on Mo carbides, although a more detailed understanding of the structure-performance relationships is needed, especially in upgrading of more complex reaction mixtures or real bio-oils.

In this work, we studied how TiO2 and ZrO2 coatings enhance the CO oxidation performance of SiO2-supported Pt catalysts under conditions relevant to automotive emissions control. SiO2 was coated with metal oxides TiO2 or ZrO2 by sol-gel method and the subsequent Pt loading was done by incipient wetness method. The prepared catalysts Pt/TiO2-SiO2 and Pt/ZrO2-SiO2 were compared with Pt/SiO2 and Pt/Al2O3 in fresh, sulfated, and hydrothermally aged states. The structure of the catalysts was characterized with BET, XRD, TEM, EDS, EXAFS, XANES, TPD and TPR to help interpret the CO oxidation performance. Higher dispersion, stability, and oxidation state of Pt were achieved on TiO2-SiO2 and ZrO2-SiO2 supports due to stronger metal-support interaction leading to superior CO oxidation performance compared to Pt/SiO2 and Pt/Al2O3. TiO2 and ZrO2 coatings introduced surface acidity but negligible basicity, which is a likely reason for the weak and low adsorption of SO2. The results suggest that the sol-gel coating of SiO2 with metal oxides could be an attractive strategy for designing automotive oxidation catalysts with enhanced performance such as low-temperature activity, sulfur tolerance, and hydrothermal stability.