Self-regeneration of supported transition metals by a high entropy-driven principle

The sintering of Supported Transition Metal Catalysts (STMCs) is a core issue during high temperature catalysis. Perovskite oxides as host matrix for STMCs are proven to be sintering-resistance, leading to a family of self-regenerative materials. However, none other design principles for self-regenerative catalysts were put forward since 2002, which cannot satisfy diverse catalytic processes. Herein, inspired by the principle of high entropy-stabilized structure, a concept whether entropy driving force could promote the self-regeneration process is proposed. To verify it, a high entropy cubic Zr0.5(NiFeCuMnCo)0.5Ox is constructed as a host model, and interestingly in situ reversible exsolution-dissolution of supported metallic species are observed in multi redox cycles. Notably, in situ exsolved transition metals from high entropy Zr0.5(NiFeCuMnCo)0.5Ox support, whose entropic contribution (TΔSconfig = T⋆12.7 J mol−1 K−1) is predominant in ∆G, affording ultrahigh thermal stability in long-term CO2 hydrogenation (400 °C, >500 h). Current theory may inspire more STWCs with excellent sintering-resistance performance.

Thermal Stability of Ru–Re NPs in H2 and O2 Atmosphere and Their Activity in VOCs Oxidation: Effect of Ru Precursor

The thermal stability of Ru–Re NPs on γ-alumina support was studied in hydrogen at 800 °C and in air at 250–400 °C. The catalysts were synthesized using Cl-free and Cl-containing Ru precursors and NH4ReO4. Very high sintering resistance of Ru–Re NPs was found in hydrogen atmosphere and independent of Ru precursors and Re loading, the size of them was below 2–3 nm. In air, metal segregation occurred at 250 °C, leading to formation of RuO2 and highly dispersed ReOx species. Ruthenium agglomeration was hindered at higher Re loading and in presence of residual Cl species. Propane oxidation rate was higher with the Ru(N)–Re catalysts than with Ru(N) and that containing Cl species. The Ru(N)–Re (3:1) catalyst exhibited the highest activity and the lowest activation energy (91.6 kJ mol−1) what is in contrast to Ru(Cl)–Re (3:1) which had the lowest activity and the highest activation energy (119.3 kJ mol−1). Thus, the synergy effect was not observed in Cl-containing catalysts. Graphic Abstract

Effect of Rare Earth Elements on Stability and Sintering Resistance of Tetragonal Zirconia for Advanced Thermal Barrier Coatings

The effect of dopant species on the sintering resistance of zirconia-based ceramics remains a huge challenge in terms of both experiment and theory. As one of the most popular materials for high-temperature protective coatings, it is still urgent to obtain rare earth-doped ZrO2 with high sintering resistance and good phase stability. Here, the sintering resistance and phase stability of rare earth oxides (La2O3, Nd2O3, Gd2O3, and Y2O3)-stabilized zirconia (ZrO2) were thoroughly studied by theoretical and experimental methods. According to experimental data, ZrO2 doped with rare earth ions with larger radii (La3+, Nd3+, and Gd3+) exhibited improved sintering resistance at reduced tetragonal phase stability. Molecular dynamics simulation results revealed that rare earth ions with larger ionic radii are prone to segregation at grain boundaries, which can more effectively reduce the grain boundary energy in the materials under consideration. Therefore, the proposed approach involving doping of NdO1.5 (~1 mol%) and YO1.5 (YbO1.5, 6 mol%) in ZrO2 is considered to be a promising route for the effective preparation of sinter-resistant ZrO2-based ceramics for refractory and thermal barrier materials.

Insights into the sintering resistance of RuO2/TiO2-SiO2 in the Deacon process: Role of SiO2

The sintering of RuO2 is a main reason for the deactivation of supported RuO2 catalysts in the oxidation of HCl to Cl2 with O2 as the oxidant, i.e., the Deacon...