Bimetallic catalysts Ag-K(Cs)/ZSM-5 for efficient soot oxidation via synergistically regulating active species and support of catalyst

Abstract

Diesel soot oxidation is a typical gas (O2)-solid (soot)-solid (catalyst) three-phase oxidation, which requires both high contact efficiency between the three-phase substances and excellent intrinsic catalytic activity of catalysts. We proposed a new strategy for improving the catalytic performances of Ag/HZSM-5 catalyst for diesel soot oxidation via synergistically regulating both active species and support of catalyst. One is constructing hierarchical pore structure on HZSM-5 (denoted as Z) support by lye treatment with various concentration (0.1 M, 0.2 M and 0.5 M); the other is incorporating alkali-metal (K or Cs) into the Ag/Z catalyst to form the bimetallic catalysts. Internally, the bimetallic catalysts Ag-K/Z-0.1 M and Ag-Cs/Z-0.1 M exhibited the superior catalytic activities. The CO2 selectivity reached 98.6% and 95.6% for Ag-K/Z-0.1 M and Ag-Cs/Z-0.1 M, respectively. In addition, Ag-Cs/Z-0.1 M obtained excellent stability, maintaining almost 100% activity without any recession after 10 cycles. Moreover, both bimetallic catalysts exhibited excellent sulfur and water resistance. The physicochemical properties of the bimetallic catalyst systems were investigated by SEM, N2 adsorption–desorption, XRD, XPS, O2-TPD, etc. The linear relationship between metallic silver and active oxygen content, and their correlation with catalysts activities have been discussed. Finally, possible dual synergistic effects in the bimetallic systems have been proposed.