RESUMEN
The increasing role of catalysis by noble metals coupled with their high price requires the development of cheaper and more effective catalysts, e.g., highly dispersed supported catalyst. Herein, Pd supported on Al2O3 catalysts prepared by deposition-precipitation under different conditions were subjected to X-ray diffraction, N2-physisorption, NH3/CO2 temperature programmed desorption, CO-chemisorption, and field-emission transmission electron microscopy analyses, which revealed that the size and distribution of Pd particles were influenced by Al2O3 support type (particle size and phase transition) and preparation conditions (metal precursor type, pH value, and solution temperature). The Pd/Al2O3 catalysts were prepared using type A (particle size = 3 micron) or type B (particle size = 20 nm) as a support and PdCl2 (PC) or Pd(NO3)2·2H2O (PN) as a Pd precursor, respectively. In XRD results, type A (particle size = 3 micron) Al2O3 had γ and î phase, and type B (particle size = 20 nm) Al2O3 had only thermally stable γ phase. In addition, Pd dispersion and crystallite size showed an obvious dependence on pH value, solution temperature and attractive/repulsive forces between the functional groups of Al2O3 and Pd precursors. Optimal results were obtained using PdCl2 (PC) as a Pd precursor and type B (particle size = 20 nm) as a support at 60 °C and pH 5.5.
RESUMEN
Hydrogenation of biomass-derived furfural is an important process in biofuel production. Herein, different Pt-supported TiO2 morphologies: nanorod (NR), nanoparticle (NP), and hollow microsphere (HMS) were prepared by the impregnation-chemical reduction method. The furfural conversion increased with an increase of Pt dispersion. However, cyclopentanone selectivity was affected by TiO2 properties, the strong metal-support interaction (SMSI) effect, and the reaction conditions. The Pt/TiO2 NR catalyst exhibited the highest cyclopentanone selectivity of 50.4%. Based on the H2-temperature programmed desorption (H2-TPD) and X-ray photoelectron spectroscopy (XPS) results, the Pt/TiO2 NR catalyst showed a SMSI effect, which was introduced by the chemical reduction method. We suggest that electron charge transfer from Ti species to Pt in the Pt/TiO2 NR catalyst affects the cyclopentanone selectivity by controlling the adsorption strength between the reactant and the Pt surface, thus retarding the formation of byproducts.
RESUMEN
We investigated the effects of Pd precursors and preparation methods on the physicochemical properties and performance of Pd/TiO2 catalysts in the photocatalytic degradation of methyl violet. To confirm the influence of the precursors, Pd/TiO2 catalysts were prepared via chemical reduction (CR) using four different Pd precursors. Additionally, to determine the effects of preparation methods, Pd/TiO2 catalysts were fabricated using K2PdCl4 precursor via three different methods: CR, deposition-precipitation (DP), and impregnation. The CO chemisorption results showed that the catalyst prepared via DP using the K2PdCl4 precursor, i.e., Pd/TiO2_K_DP, displayed the highest Pd dispersion of 12.42% owing to the stable formation of Pd(OH)2, which strongly interacted with the -OH groups on the TiO2 support. Although the catalyst prepared via CR using the Pd(NH3)4Cl2·H2O (PA) precursor, i.e., Pd/TiO2_PA_CR, had the lowest Pd dispersion of 0.7%, it exhibited the highest absorption of 26% after 30 min in the dark. It was found that high Pd2+/Pd0 ratio in dark conditions adversely affected the absorption of MV owing to electrostatic repulsion between the cationic dyes and metal nanoparticles. However, the Pd dispersion and the specific surface area played a key role in the photocatalytic activity under UV irradiation. Pd/TiO2_K_CR with higher Pd dispersion showed the highest photocatalytic activity and reaction rate of 0.0212 min-1.