The oxidation stability of a low surface area Mo2C catalyst has been studied in the presence of gases associated with the steam and dry (CO2) reforming of methane, at temperatures up to 850°C and pressures to 8 bar. The oxidation onset temperatures were found to be about 600°C when the carbide was exposed to either steam or CO2. There appears to be two distinct mechanisms for Mo2C oxidation: direct oxidation at low temperatures and thermal decomposition followed by oxidation of the Mo metal at temperatures above 750°C. Although onset temperatures were similar, CO2 was a stronger oxidant than steam at the higher temperatures. Both H2 and CO were found to inhibit oxidation and the effect can be explained by their influence on the prevailing kinetics. Trace concentrations of methane were found to completely stabilize the carbide from steam oxidation but significantly higher concentrations were required to stabilize it from CO2 oxidation and this is attributed to the higher rates of CO2 oxidation relative to carburization rates. The effect of pressure on the onset temperature of CO2 oxidation of the carbide was found to be negligible, even when inhibited by CO.

This edited book provides an in-depth overview of carbon dioxide (CO2) transformations to sustainable power technologies. It also discusses the wide scope of issues in engineering avenues, key designs, device fabrication, characterizations, various types of conversions and related topics. It includes studies focusing on the applications in catalysis, energy conversion and conversion technologies, etc. This is a unique reference guide, and one of the detailed works is on this technology. The book is the result of commitments by leading researchers from various backgrounds and expertise. The book is well structured and is an essential resource for scientists, undergraduate, postgraduate students, faculty, R&D professionals, energy chemists and industrial experts.

In this paper, 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. Finally, 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.

One of the most prominent challenges facing the commercialization of the direct methanol fuel cell (DMFC) is the high cost of its electrocatalyst components, particularly the anode. The anode typically requires a high loading of precious metal electrocatalyst (Pt-Ru) to obtain a useful amount of electrical energy from the electrooxidation of methanol (CH 3 OH). The complete electrooxidation of methanol on these catalysts produces strongly adsorbed CO on the surface, which reduces the activity of Pt. The presence of Ru in these electrocatalysts assists with the decomposition of H 2 O to more efficiently remove the poisoning CO species as CO 2 (g). The primary disadvantage of these electrocatalyst components is the scarcity and consequently high price of both Pt and Ru. A series of surface science studies ultrahigh vacuum (UHV) have identified molybdenum and tungsten carbide materials as potential alternative DMFC anode electrocatalysts. Both of these materials demonstrated activity towards the decomposition of methanol and water molecules. The purpose of this research was to extend these investigations by the synthesis and characterization of more realistic carbide materials. This was accomplished by a combination of surface science and electrochemical experiments. The electrochemical studies were performed both in-situ and ex-situ in order to better address the "materials gap" and "pressure gap" that often separate findings in UHV studies from results in more realistic environments. Thin film surfaces of molybdenum carbide could be produced on various carbon substrates in a vacuum system by physical vapor deposition (PVD). When modified with low coverages of Pt, MoC phase molybdenum carbides were found to be more active towards the electrooxidation of hydrogen in an acidic electrolyte than Ptmodified carbon substrates in cyclic voltammetry (CV) studies. These surfaces demonstrated a limited range of electrochemical stability in this acid solution. Mo 2 C surfaces have previously shown hydrogen electrooxidation activity, but demonstrated a nearly identical stability range to MoC in an identical electrolyte. Within these stable ranges of operation, neither surface demonstrated activity towards methanol electrooxidation. These surfaces are also found to undergo rapid decomposition at higher operating potentials, which could be disadvantageous for use in DMFC's. Despite these findings for molybdenum carbides, in-situ CV studies reveal that tungsten monocarbides (WC) show significant activity towards methanol oxidation in acidic solution and a larger range of stability. Steady-state Chronoamperometry (CA) measurements show an enhanced performance for methanol electrooxidation on WC and sub-monolayer Pt-modified WC surfaces by comparison with Pt surfaces. Surface science studies demonstrate that the WC and Pt-modified WC surfaces remained stable during the CA measurements. To further bridge the materials and pressure gaps mentioned earlier, polycrystalline thin films of WC were synthesized on various carbon substrates commonly used in fuel cell applications. The activity of WC and Pt-modified WC PVD films surfaces towards methanol and adsorbed CO species in ex-situ CV experiments enabled a discussion of the advantages and limitations of the WC electrocatalyst when produced using larger scale synthesis methods. To further aid this investigation, WC nanomaterials with and without Pt-modification were integrated as the anode electrocatalyst in DMFC devices. These fuel cells were used in a preliminary study to identify the most basic performance characteristics of the anode. Additionally, these findings motivate a discussion of the relative ease with which WC-based electrocatalysts may be integrated into fuel cells using proven fabrication techniques.