Improved catalytic activity over P-doped ceria-zirconia-alumina supported palladium catalysts for methane oxidation

The Effect P Additive on the CeZrAl Support Properties and the Activity of the Pd Catalysts in Propane Oxidation

The properties of a catalyst support are closely related to the catalyst activity, yet the focus is often placed on the active species, with little attention given to the support properties. In this work, we specifically investigated the changes in support properties after the addition of P, as well as their impact on catalyst activity when used for catalyst preparation. We prepared the CeO2-ZrO2-P2O5-Al2O3 (CeZrPAl) composite oxides using the sol-gel, impregnation, and mechanical mixing methods, and characterized the support properties using techniques such as XRD, XPS, SEM-EDS, N2 adsorption-desorption, and Raman spectra. The results showed that the support prepared using the sol-gel method can exhibit a more stable phase structure, larger surface area, higher adsorption capacity for oxygen species, and greater oxygen storage capacity. The addition of an appropriate amount of P is necessary. On the one hand, the crystallization and growth of CePO4 can lead to a decrease in the Ce content in the cubic phase ceria-zirconia solid solution, resulting in a phase separation of the ceria-zirconia solid solution. On the other hand, CePO4 can lock some of the Ce3+/Ce4+ redox pairs, leading to a reduction in the adsorption of oxygen species and a decrease in the oxygen storage capacity of the CeZrPAl composite oxides. The research results indicated that the optimal P addition is 6 wt.% in the support. Therefore, we prepared a Pd/CeZrPAl catalyst using CeZrAl with 6 wt.% P2O5 as the support and conducted the catalytic oxidation of C3H8. Compared with the support without P added, the catalyst activity of the support loaded with P was significantly improved. The fresh and aged (1000 °C/5 h) catalysts decreased by 20 °C and 5 °C in T50 (C3H8 conversion temperature of 50%), and by 81 °C and 15 °C in T90 (C3H8 conversion temperature of 90%), respectively.

Catalytic Oxidation of n-Decane, n-Hexane, and Propane over Pt/CeO2 Catalysts

Pt species with different chemical states and structures were supported on CeO₂ by solution reduction (Pt/CeO₂-SR) and wet impregnation (Pt/CeO₂-WI) and investigated in catalytic oxidation of n-decane (C₁₀H₂₂), n-hexane (C₆H₁₄), and propane (C₃H₈). Characterization by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, H₂-temperature programming reduction, and oxygen temperature-programmed desorption showed that Pt⁰ and Pt²⁺ existed on Pt nanoparticles of the Pt/CeO₂-SR sample, which promoted redox, oxygen adsorption, and activation. On Pt/CeO₂-WI, Pt species were highly dispersed on CeO₂ as the Pt-O-Ce structure, in which surface oxygen decreased significantly. The Pt/CeO₂-SR catalyst presents high activity in oxidation of C₁₀H₂₂ with a rate of 0.164 μmol min^-1 m^-2 at 150 °C. The rate increased with oxygen concentration. Moreover, Pt/CeO₂-SR presents high stability on feed stream containing 1000 ppm C₁₀H₂₂ at gas hour space velocity = 30,000 h^-1 as low as 150 °C for 1800 min. The low activity and stability of Pt/CeO₂-WI were probably related to its low availability of surface oxygen. In situ Fourier transform infrared results showed that the adsorption of alkane occurred through the interaction with Ce-OH. The adsorption of C₆H₁₄ and C₃H₈ was much weaker than that of C₁₀H₂₂, which resulted in the decrease in activity for C₆H₁₄ and C₃H₈ oxidation of Pt/CeO₂ catalysts.

Development of a New Ternary Al2O3-HAP-Pd Catalyst for Diethyl Ether and Ethylene Production Using the Preferential Dehydration of Ethanol

This study aims to convert ethanol to higher value-added products, particularly diethyl ether and ethylene using the catalytic dehydration of ethanol. Hence, the gas-phase dehydration of ethanol over Al2O3-HAP catalysts as such and modified by addition of palladium (Pd) in a microreactor was evaluated. The commercial Al2O3-HAP catalyst was first prepared by the physical mixing method, and then, the optimal ratio of the Al2O3-HAP catalyst (2:8 by wt %) was impregnated with Pd to develop a new functional catalyst to alter surface acidity. Based on the results, the combination of Al2O3 and HAP catalysts generated significant quantities of weak acid sites which demonstrates an enhancement in catalytic activity. In addition, Pd modification in the optimal composition ratio of the Al2O3-HAP catalyst extremely increased the amount of weak acid sites as well as weak acid density due to the synergistic effect between the Pd and Al2O3-HAP catalyst that are supposed to suggest the active sites in the reaction. Among all catalysts, the Al20-HAP80-Pd catalyst displayed brilliant catalytic performance in the course of diethyl ether yield (ca. 51.0%) at a reaction temperature of 350 °C and ethylene yield (ca. 75.0%) at a reaction temperature of 400 °C having an outstanding stability under time-on-stream for 10 h. This is recognized to the combination of the effects of weak acid sites (Lewis acidity), small amount of strong acid sites, and structural characteristics of the catalytic materials used.

Size effects of Pd nanoparticles supported over CeZrPAl for methane oxidation

Pd nanoparticles accompanied with distorted morphology result in considerable active sites and enhance the intrinsic activity for catalytic methane oxidation.