Final Report

White, John M.

University of Texas at Austin

关键词: Desorption;    37 Inorganic, Organic, Physical And Analytical Chemistry;    Thermodynamic Activity;    Oxidation;    Transition Elements;   

DOI  :  10.2172/902521
RP-ID  :  DOE/ER15480-final
RP-ID  :  FG02-03ER15480
RP-ID  :  902521

美国|英语

来源: UNT Digital Library

【 摘 要 】

Under our grant, DE-FG02-03ER15480, "Early transition metal oxides as catalysts: crossing scales from clusters to single crystals to functioning materials," catalytic activity of high surface area, powdered transition metal oxides (TMO, e.g. vanadium, niobium, molybdenum, and tungsten) supported on Al2O3, SiO2, ZrO2 and TiO2 have been extensively studied. In contrast, virtually no studies have been conducted for TMOs supported on well-ordered, single-crystalline oxides. This is largely due to a number of experimental difficulties related to the preparation of well-ordered oxide surfaces and to the charging problems associated with electron based probes on insulators. In our experiments we have selected TiO2(110) as a well-ordered substrate. TiO2(110) is a semiconductor (EG = 3.0 eV) and as such it has been extensively studied using ensemble averaged, as well as atomically resolved probes.1 In this work our goal was to create a well characterized, WO3/TiO2(110) model catalyst and interrogate its chemical activity for reactions of interest to this program. Initial studies of the chemical activity of the WO3 clusters on TiO2(110) focused on the partial oxidation of CH3OH. Only molecular desorption of CH3OH was observed. For 1 ML of CH3OH adsorbed on clean TiO2(110), the fraction of CH3OH desorbing from Ti4+ (250-400K) and BBO (150-250 K) sites is approximately the same, similar to H2O desorption. For CH3OH desorption from WO3/TiO2(110), a larger fraction of CH3OH desorbs from oxygen terminated sites, suggesting that the Ti4+ sites were covered by WO3. Current studies of alcohol oxidation reactions focus on the higher alcohols, such as 2-propanol and 2?butanol. In other studies, we have explored the adsorption of formaldehyde as one of the potential products in the partial oxidation of CH3OH. A catalytic polymerization reaction resulting in the formation of trioxane (paraformaldehyde) was observed.