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

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 CO2 desorption (TPD-MS) at 170 degrees C and at about 620 degrees C due to a surface carbonates decomposition. The thermodesorption of oxygen at 650-850 degrees C indicates the decomposition of AgOx phases at the surface. The presence of AgOx phases is also confirmed by TPR-H2 spectrum (low temperature reduction peak at 130 and 180 degrees C). The high-temperature reduction at about 570 degrees C is probably related to Ag-O-M phases on the support. The soot combustion takes place at T-50=575 degrees C. Without silver (sepiolite-Zr-K-O) T-50=560 degrees C but sepiolite modified with silver (sepiolite-Zr-K-Ag-O) undergoes the same process at T-50=490 degrees C. (C) 2006 Elsevier B.V. All rights reserved.