Synthesis and molecular structure of model silica-supported tungsten oxide catalysts for oxidative coupling of methane (OCM)

Catalysts with only dispersed phase Na–WO₄ sites where Na/W < 2 are slightly less active but significantly more C₂ selective than the traditional Na₂WO₄/SiO₂ catalysts that contain a crystalline phase where Na/W = 2.

Strong Metal-Support Interactions between Copper and Iron Oxide during the High-Temperature Water-Gas Shift Reaction

The commercial high-temperature water-gas shift (HT-WGS) catalyst consists of CuO-Cr₂ O₃ -Fe₂ O₃ , where Cu functions as a chemical promoter to increase the catalytic activity, but its promotion mechanism is poorly understood. In this work, a series of iron-based model catalysts were investigated with in situ or pseudo in situ characterization, steady-state WGS reaction, and density function theory (DFT) calculations. For the first time, a strong metal-support interaction (SMSI) between Cu and FeO_x was directly observed. During the WGS reaction, a thin FeO_x overlayer migrates onto the metallic Cu particles, creating a hybrid surface structure with Cu-FeO_x interfaces. The synergistic interaction between Cu and FeO_x not only stabilizes the Cu clusters, but also provides new catalytic active sites that facilitate CO adsorption, H₂ O dissociation, and WGS reaction. These new fundamental insights can potentially guide the rational design of improved iron-based HT-WGS catalysts.

Pyrolysis of the Cellulose Fraction of Biomass in the Presence of Solid Acid Catalysts: An Operando Spectroscopy and Theoretical Investigation

Biomass pyrolysis by solid acid catalysts is one of many promising technologies for sustainable production of hydrocarbon liquid fuels and value-added chemicals, but these complex chemical transformations are still poorly understood. A series of well-defined model SiO₂ -supported alumina catalysts were synthesized and molecularly characterized, under dehydrated conditions and during biomass pyrolysis, with the aim of establishing fundamental catalyst structure-activity/selectivity relationships. The nature and corresponding acidity of the supported AlO_x nanostructures on SiO₂ were determined with ²⁷ Al/¹ H NMR and IR spectroscopy of chemisorbed CO, and DFT calculations. Operando time-resolved IR-Raman-MS spectroscopy studies revealed the molecular transformations taking place during biomass pyrolysis. The molecular transformations during biomass pyrolysis depended on both the domain size of the AlO_x cluster and molecular nature of the biomass feedstock. These new insights allowed the establishment of fundamental structure-activity/selectivity relationships during biomass pyrolysis.

Nature of Active Sites and Surface Intermediates during SCR of NO with NH₃ by Supported V₂O₅--WO₃/TiO₂ Catalysts

Time-resolved in situ IR was performed during selective catalytic reduction of NO with NH₃ on supported V₂O₅-WO₃/TiO₂ catalysts to examine the distribution and reactivity of surface ammonia species on Lewis and Brønsted acid sites. While both species were found to participate in the SCR reaction, their relative population depends on the coverage of the surface vanadia and tungsta sites, temperature, and moisture. Although the more abundant surface NH₄⁺_,ads intermediates dominate the overall SCR reaction, especially for hydrothermally aged catalysts, the minority surface NH_3,ads intermediates exhibit a higher specific SCR activity (TOF). The current study serves to resolve the long-standing controversy about the active sites for SCR of NO with NH₃ by supported V₂O₅-WO₃/TiO₂ catalysts.