CO Oxidation Efficiency and Hysteresis Behavior over Mesoporous Pd/SiO2 Catalyst

Abstract

Carbon monoxide (CO) oxidation is considered an important reaction in heterogeneous industrial catalysis and has been extensively studied. Pd supported on SiO2 aerogel catalysts exhibit good catalytic activity toward this reaction owing to their CO bond activation capability and thermal stability. Pd/SiO2 catalysts were investigated using carbon monoxide (CO) oxidation as a model reaction. The catalyst becomes active, and the conversion increases after the temperature reaches the ignition temperature (Tig). A normal hysteresis in carbon monoxide (CO) oxidation has been observed, where the catalysts continue to exhibit high catalytic activity (CO conversion remains at 100%) during the extinction even at temperatures lower than Tig. The catalyst was characterized using BET, TEM, XPS, TGA-DSC, and FTIR. In this work, the influence of pretreatment conditions and stability of the active sites on the catalytic activity and hysteresis is presented. The CO oxidation on the Pd/SiO2 catalyst has been attributed to the dissociative adsorption of molecular oxygen and the activation of the C-O bond, followed by diffusion of adsorbates at Tig to form CO2. Whereas, the hysteresis has been explained by the enhanced stability of the active site caused by thermal effects, pretreatment conditions, Pd-SiO2 support interaction, and PdO formation and decomposition.

A Novel Metal-Containing Mesoporous Silica Composite for the Decolorization of Rhodamine B: Effect of Metal Content on Structure and Performance

“…The Si–O band always appears around 461 cm –1 , which here is covered by stretching vibration of the metal-oxygen bond in the range of 469 cm –1 ~480 cm –1 [ 18 , 23 ]. Soubaihi R. et al, 2021 studied Pd/SiO 2 Catalyst characteristics, and similar peaks for SiO 2 have been reported [ 28 ].…”

Activity and Thermal Aging Stability of La1−xSrxMnO3 (x = 0.0, 0.3, 0.5, 0.7) and Ir/La1−xSrxMnO3 Catalysts for CO Oxidation with Excess O2

“…Such hysteresis phenomena are not uncommon in heterogeneous catalysis, especially in CO oxidation catalysis, where in many cases these are followed by isothermal self-sustained oscillations [ 1 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 57 , 58 ]. Among other considerations, the origin of the hysteresis and oscillatory phenomena can be attributed to changes in the oxidation state and/or restructuring of the active phase.…”

“…In addition, as a reaction with the absence of by-products, it is often used as a probe system for evaluating a wide variety of innovative catalysts [ 11 , 12 ]. However, at the same time, the catalytic oxidation of CO is a perfect example of a very complex reaction in terms of mechanistic behavior, which depending on the conditions can exhibit steady-state multiplicity, oscillatory or even chaotic behavior [ 1 , 8 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. All the above rank this reaction as one of the most studied in heterogeneous catalysis, which continues with undiminished interest even today.…”

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“…Interestingly, a structure-activity relationship was proposed, correlating the catalyst activation and CO oxidation hysteresis behavior with the information on both the palladium oxidation states and nanoparticle dispersion. In particular, the best low-temperature CO oxidation performance was achieved by calcining the catalyst at 450 • C [25].…”