Effect of χ-alumina addition on H 2 S oxidation properties of pure and modified γ-alumina

Carbide-Induced Thermal Shock Synthesis of High-Entropy Alloy Nanoparticles Anchored on WO3 Nanofibers for High-Performance Gas Sensors

The synthesis of high-entropy alloy nanoparticles (HEA NPs) on oxide supports with a uniform and homogeneous distribution has been a significant challenge in traditional carbothermal shock (CTS) methods. In this study, we introduce a carbide-induced thermal shock (CITS) process for synthesizing HEA NPs anchored on tungsten trioxide (WO3) nanofibers. Utilizing one-dimensional (1D) tungsten carbide (WC) nanofibers (NFs) as scaffolds, we facilitated their oxidation to WO3 while preserving structural integrity. This approach resulted in the formation of ultrasmall HEA NPs (1-3 nm) strongly anchored on the WO3 NFs, preventing grain growth and enabling a core-shell microstructure. The functionalized WO3 NFs with homogeneously distributed HEA NPs demonstrated significantly enhanced gas sensing performance, especially for hydrogen sulfide (H2S), with a response (Rair/Rgas) of 22.1 at 5 ppm. This improvement is attributed to the CITS process, which enhances the chemisorption of oxygen species and increases the density of Lewis acid sites, leading to superior catalytic performance and stability. The findings from this study demonstrate the effectiveness of the CITS method in synthesizing highly active oxide-based catalysts and its potential applications in advanced gas sensing technologies under extreme conditions.

Spectroscopic Study of Five-Coordinated Thermal Treated Alumina Formation: FTIR and NMR Applying

This work represents research into materials designed to improve the environment. The study was carried out on aluminum hydroxide xerogels and alumina catalysts obtained by the Controlled Double Jet Precipitation (CDJP) process at different pH values. It has been shown that the pH of the CDJP process determines the content of aluminum-bound nitrate ions in the aluminum hydroxide. These ions are removed at a higher temperature than the decomposition of ammonium nitrate. The high content of aluminum-bound nitrate ions determines the structural disorder of the alumina and the high content of the penta-coordinated alumina catalyst.

Engineering of crystal phase over porous MnO2 with 3D morphology for highly efficient elimination of H2S

In the present work, we report a facile oxalate-derived hydrothermal method to fabricate α-, β- and δ-MnO₂ catalysts with hierarchically porous structure and study the phase-dependent behavior for selective oxidation of H₂S over MnO₂ catalysts. It was disclosed that the oxygen vacancy, reducibility and acid property of MnO₂ are essentially determined by the crystalline phase. Systematic experiments demonstrate that δ-MnO₂ is superior in active oxygen species, activation energy and H₂S adsorption capacity among the prepared catalysts. As a consequence, δ-MnO₂ nanosphere with a hierarchically porous structure shows high activity and stability with almost 100% H₂S conversion and sulfur selectivity at 210 °C, better than majority of reported Mn-based materials. Meanwhile, hierarchically porous structure of δ-MnO₂ nanosphere alleviates the generation of by-product SO₂ and sulfate, promoting the adoptability of Mn-based catalysts in industrial applications.

Effect of the Addition of Alkaline Earth and Lanthanide Metals for the Modification of the Alumina Support in Ni and Ru Catalysts in CO2 Methanation

In order to reduce greenhouse gas emissions, which are reaching alarming levels in the atmosphere, capture, recovery, and transformation of carbon dioxide emitted to methane is considered a potentially profitable process. This transformation, known as methanation, is a catalytic reaction that mainly uses catalysts based on noble metals such as Ru and, although with less efficiency, on transition metals such as Ni. In order to improve the efficiency of these conventional catalysts, the effect of adding alkaline earth metals (Ba, Ca, or Mg at 10 wt%) and lanthanides (La or Ce at 14 wt%) to nickel (13 wt%), ruthenium (1 wt%), or both-based catalysts has been studied at temperatures between 498 and 773 K and 10 bar pressure. The deactivation resistance in presence of H2S was also monitored. The incorporation of La into the catalyst produces interactions between active metal Ni, Ru, or Ru-Ni and the alumina support, as determined by the characterization. This fact results in an improvement in the catalytic activity of the 13Ni/Al2O3 catalyst, which achieves a methane yield of 82% at 680 K for 13Ni/14La-Al2O3, in addition to an increase in H2S deactivation resistance. Furthermore, 89% was achieved for 1Ru-13Ni/14La-Al2O3 at 651 K, but it showed to be more vulnerable to H2S presence.

A study of deactivation by H2S and regeneration of a Ni catalyst supported on Al2O3, during methanation of CO2. Effect of the promoters Co, Cr, Fe and Mo

Energy storage from renewable sources is possible by chemical procedures, power to gas technology being a possible solution for long-term storage. In this work, CO₂ methanation from a sulphur containing gas was studied, taking into account deactivation of the catalysts and a regeneration process. In order to improve the sulphur resistance of a standard nickel (13%) catalyst supported on alumina, transition metals like molybdenum (Mo), iron (Fe), cobalt (Co) or chromium (Cr), in different proportions (from 4 to 8 wt%) were added to the catalyst formulation. The catalyst activity, between 573 and 773 K, at 10 bar, increased when transition metals were added except for Mo in the highest proportion. These bimetallic catalysts presented a similar deactivation resistance than the monometallic catalyst when sulphur was present in the feed. Once H₂S was removed from the feed, and the catalysts regenerated with oxygen, only the catalyst containing cobalt recovered up to a 13% methane yield.

Energy storage from renewable sources is possible by chemical procedures, power to gas technology being a possible solution for long-term storage.