Acid sites on silica-supported molybdenum oxides probed by ammonia adsorption: Experiment and theory

A study of molybdena catalysts in ethanol oxidation. Part 1. Unsupported and silica‐supported MoO3

“…These data show that acetaldehyde is the main primary product and its production can be tentatively assigned to the presence of Mo, acting as a redox catalyst; 42 however, at high temperatures classical dehydration products arising from catalyst acidity were detected, suggesting that weak acid sites were present on the catalysts and a contribution may be attributed to the well-known Brønsted acidity of Mo. 45,46 The results show that the yield in acetaldehyde obtained over our catalysts may be lower than that obtained on some vanadia-based catalysts. 23,24 However, in our case, the only observed by-product was ethylene, which in principle may be quite easily recovered as a useful product, with only traces of CO 2 .…”

“…Several authors 26,44 reported on the significant acidity of MoO 3 /SiO 2 due to the presence of Brønsted acidity generated just by the interaction of molybdena with silica. 45 However, this interpretation is not very convincing because the presence of molybdena induces Brønsted acidity and stronger Lewis acidity also on other oxide supports such as for MoO 3 /TiO 2 catalysts 46 and MoO 3 /ZrO 2 , 47,48 and results in Brønsted acidity on alumina as well. 49 The presented catalytic data, pointing out an extensive production of ethylene from ethanol at 570 K, show that acidity is a property even of pure molybdena.…”

Olefin-surface interactions modulate the activity of silica-supported Mo-based olefin metathesis catalysts

“…For instance, interactions of functionalized olefins containing ester groups and surface silanol groups were recently found to enrich the near-surface concentration of olefins and influence product selectivities for ring-closing metathesis reactions catalyzed by well-defined cationic Mo alkylidenes supported on mesoporous silicas. 60 The silica-supported Mo oxo system is known to possess strong Brønsted acid sites that could act as adsorption sites, 61 and even on pure silica the interaction energies of hydrocarbons are known to increase as a function of chain length and are greater for alkenes than alkanes. 62 The catalytic reaction tests and solid-state NMR analyses discussed above show that substrate-silica interactions are non-negligible even for long-chain olefinic hydrocarbons and indeed have significant effects on catalytic reaction properties at low reaction temperatures (<100 °C).…”

Oxidation Protection of High-Temperature Coatings on the Surface of Mo-Based Alloys—A Review

“…Molybdenum and molybdenum-based alloys have a high melting point (2620 • C), good high-temperature mechanical properties and high conductivity and thermal conductivity, and are widely used in high-temperature structures [5][6][7][8][9][10]. However, the alloys have a poor oxidation resistance, and the "Pesting oxidation" at 400-800 • C and oxidation decomposition above 1000 • C are the main factors that limit their application [11][12][13][14]. At present, the alloying and surface-coating technology are the main methods to increase the oxidation resistance of the basal materials [15,16].…”