Eliciting a Synergistic Effect between Mixed Metal Oxides and Metallic Pt Nanoparticles for Active and Stable Catalysts

Cold start exhaust from vehicular internal combustion engines contributes significantly to the total portion of vehicle emissions, yet modern emission control catalysts still rely on high exhaust temperatures to reach peak catalytic activity while being sensitive to sintering at the elevated operating conditions. Altering the physical support structure to utilize geometric effects can stabilize catalytic active phases. Alterations to electronic effects through manipulating the support chemical composition can improve the performance with lower temperatures to reach required pollutant conversion. In this study we probe how tuning the chemical composition of an encapsulated metal oxide system where platinum nanoparticles are encapsulated in mixed alumina and manganese oxide layers (Pt@xAl2O3/yMnOx) can provide a synergistic effect in increasing both catalytic activity and stability for carbon monoxide (CO) oxidation. Testing and aging of catalysts with different Al2O3/MnOx ratios (1/0, 3/1, 1/1, 1/3, and 0/1) revealed that some samples could outperform single metal oxide catalysts in both activity and stability metrics. Pt@3Al2O3/1MnOx, after a 1000 °C aging treatment in the presence of CO and in oxidizing conditions, showed a CO2 production rate at least 18 times larger than any other sample. It also demonstrated the least amount of deactivation after the 1000 °C aging treatment, its CO2 production rate decreased by 1.8 times, whereas the Pt@1Al2O3/1MnOx and Pt@1Al2O3/3MnOx samples recorded rate decreases of 310 and 1300 times, respectively. Based on these trends, we hypothesized that an alumina-rich sample could provide the optimal balance between stability and activity. A Pt@9Al2O3/1MnOx catalyst was thus synthesized and not only did not deactivate but also demonstrated an improvement in activity after aging, proving to be more than 88 times as active compared to Pt@Al2O3 aged at the same 1000 °C condition. This work proves that by optimizing the content of the aluminum and manganese mixed oxide in an encapsulated support, a synergistic restructuring of the support and Pt nanoparticles created a stable and active CO oxidation catalyst.