Stable Performance of Supported PdOx Catalyst on Mesoporous Silica-Alumina of Water Tolerance for Methane Combustion under Wet Conditions

Abstract

In methane combustion, water tolerance of Pd-based catalysts is quite critical for stable performance, because water is produced in situ and a water-containing feed is used under real conditions. Herein, water-tolerant mesoporous silica-alumina (H-MSA) was prepared by solvent deficient precipitation (SDP) using triethoxy(octyl)silane (TEOOS) and aluminum isopropoxide (AIP). The H-MSA was more tolerant to water than γ-alumina, mesoporous alumina (MA), and mesoporous silica-alumina (MSA) synthesized by using tetraethyl orthosilicate (TEOS), because of the silica present on the external particle surface. Moreover, it exhibited better textural properties, leading to higher dispersion of PdOx. The PdOx catalyst supported on H-MSA was quite durable in repeated temperature-programmed cycles and isothermal tests in the presence of water vapor, compared to the reference PdOx catalysts. The measured stability was attributed to the water tolerance, weak Lewis acidity, and penta-coordinated Al species of the H-MSA support, which was preferentially imparted when TEOOS was added for substitution of 5 mol% AIP for the synthesis of H-MSA. Therefore, the SDP method employed herein is useful in endowing supported PdOx catalysts with the water tolerance necessary for stable methane combustion performance under wet conditions.

Mesoporous Acidic SiO2–Al2O3 Support Boosts Nickel Hydrogenation Catalysis for H2 Storage in Aromatic LOHC Compounds

“…Finally, H 2 reduction was performed at 600 °C in a H 2 flow for 5 h. It is noteworthy that the above conditions were determined through preliminary works to attain higher Ni dispersion (Figure S1). First, using tetrahydrofuran as a solvent led to a decrease in the average Ni particle size ( D Ni ) because the prepared MSA supports are highly hydrophobic, e.g., D Ni of 5.0 nm for Ni/MSA_C 8 TES prepared using water vs D Ni of 3.5 nm for Ni/MSA_C 8 TES prepared using tetrahydrofuran. Next, air calcination was avoided because of strong agglomeration of Ni nanoparticles: the measured D Ni was 6.9 nm for Ni/MSA_C 8 TES calcined at 550 °C followed by H 2 reduction at 600 °C.…”

“…In this respect, solvent-deficient precipitation (SDP) is interesting because it can provide significant mesoporosity without addition of structure-directing agents, e.g., mesoporous alumina (MA) synthesized using aluminum isopropoxide (AIP). , The MA was also reported to show improved metal dispersion and catalyst stability by strong metal–support interaction . Moreover, the addition of SiO 2 into MA was achieved by initially mixing AIP with TEOS or octyltriethoxysilane (C 8 TES) . These reports intrigued us to try synthesizing the SiO 2 –Al 2 O 3 by the SDP method using AIP and C n TES with different lengths of the alkyl substituent because the alkyl substituent affects the ratio of condensation and cyclization rates in sol–gel synthesis .…”