Structure–Activity Relationships of WOx-Promoted TiO2–ZrO2 Solid Acid Catalyst for Acetalization and Ketalization of Glycerol towards Biofuel Additives

Abstract: WOx-promoted TiO2–ZrO2 solid acid catalyst was prepared and applied in the catalytic acetalization and ketalization of glycerol with carbonyl compounds to produce biofuel additives. The presence of WOx promoter and TiO2 remarkably improved the catalytic activity of ZrO2. Approximately, 100% glycerol conversion was evidenced with non-bulky aliphatic aldehydes and ketones like, propanol and cyclohexanone. The physical characterization of WOx-promoted TiO2–ZrO2, revealed a higher formation of tetragonal crystalline phase of ZrO2, over monoclinic. The total surface acidity and the ratio of Brønsted to Lewis acidic site concentrations were determined by NH3-TPD and pyridine-chemisorbed FTIR spectroscopy, respectively. A considerably higher concentration of Lewis acidic sites, ~ 213.29 μmol/gm, was evidenced on the WOx-promoted TiO2–ZrO2 catalyst surface. Catalytic activity study revealed a direct correlation between the surface Lewis acidic site concentration and the activity of catalyst. This significant observation indicated the key role of Lewis acidic sites in this catalytic process. The WOx-promoted TiO2–ZrO2 catalyst was also considerably stable and showed good performance in the acetalization/ketalization of glycerol with other substituted carbonyl compounds. Graphic Abstract: The WOx-promoted TiO2–ZrO2 solid acid catalyst exhibits superior catalytic performance for acetalization and ketalization of glycerol with carbonyl compounds to produce biofuel additives. [Figure not available: see fulltext.]. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature

Investigation on the physicochemical properties of Ce0.8Eu0.1M0.1O2−δ (M = Zr, Hf, La, and Sm) solid solutions towards soot combustion

This investigation focuses on the manipulation of the physicochemical properties and oxygen defect concentration of europium doped CeO2 by the introduction of a second dopant (co-dopant, M). Accordingly, in this study a series of Ce0.8Eu0.1M0.1O2-delta (M = Zr, Hf, La, and Sm) nano-oxides were prepared and tested for diesel soot oxidation catalysis. The systematic characterization studies indicated successful incorporation of both dopants in the cubic fluorite crystal structure of CeO2. A remarkable enhancement in the reduction properties and oxygen defect concentration was observed for the co-doped samples from structural and chemical analyses. The aliovalent co-doped materials exhibited better performance than the isovalent co-doped materials. The catalytic activity order of the prepared materials towards model soot oxidation was Ce0.8Eu0.1La0.1O2-delta > Ce0.8Eu0.1Sm0.1O2-delta > Ce0.8Eu0.1Hf0.1O2-delta > Ce0.8Eu0.1Zr0.1O2-delta > Ce0.9Eu0.1O2-delta > CeO2. The most favorable modification of the physicochemical properties of europium doped ceria was ascertained in the presence of La as a co-dopant compared to other combinations investigated. The correlation of the physicochemical properties with the catalytic activity has also been clearly demonstrated in the manuscript

Superior catalytic performance of a CoOx/Sn–CeO2 hybrid material for catalytic diesel soot oxidation

The present work reports the synthesis and characterization of a ceria-based hybrid nano-catalyst composed of a Snx+ dopant incorporated in the CeO2 crystal lattice and a finely dispersed CoOx phase on its surface. Characterization studies showed that the Ce, Sn, and Co cations were present in their multivalent oxidation states. The CoOx was confirmed to be Co3O4. A HRTEM image depicted the presence of a stepped catalyst surface, which has a special importance in enhancing the heterogeneous catalytic reaction rate carried out on the solid catalyst surface. The prepared materials were subjected to diesel soot oxidation catalysis. Model soot was combusted in the presence of air under both tight and loose contact conditions of the catalyst and soot. The hybrid catalyst exhibited improved performance compared to the Sn-doped nano-CeO2 and nano-CeO2 supported CoOx catalysts. The improved catalytic activity was attributed to the existence of synergism among the multivalent cations and the stepped surface of the hybrid catalyst, which act as the potential active sites for oxidation catalysis