Characterization of sepiolite as a support of silver catalyst in soot combustion

摘要

Turkish sepiolite-zirconium oxide mixtures were applied as a support for the silver catalyst in a soot combustion. Sepiolite-Zr-K-Ag-O catalyst was characterized by XRD, N_2 adsorption, SEM, TPR-H_2 and EGA-MS. The combustion of soot was studied with a thermobalance (TG-DTA). The modification resulted in a partial degradation of the sepiolite structure, however, the morphology was preserved. The adsorption of N_2 of the modified sepiolite is a characteristic for mesoporous materials with a wide distribution of pores. The specific surface area S_(BET) equals 83 m~2/g and the pores volume is 0.23 cm~3/g. The basic character of the surface centers of sepiolite is indicated by CO_2 desorption (TPD-MS) at 170℃ and at about 620℃ due to a surface carbonates decomposition. The thermodesorption of oxygen at 650-850℃ indicates the decomposition of AgO_x phases at the surface. The presence of AgO_x phases is also confirmed by TPR-H_2 spectrum (low temperature reduction peak at 130 and 180℃). The high-temperature reduction at about 570℃ is probably related to Ag-O-M phases on the support. The soot combustion takes place at T_(50)=575℃. Without silver (sepiolite-Zr-K-O) T_(50)=560℃ but sepiolite modified with silver (sepiolite-Zr-K-Ag-O) undergoes the same process at T_(50)=490℃.