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, N2 adsorption, SEM, TPR-H2 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 N2 of the modified sepiolite is a characteristic for mesoporous materials with a wide distribution of pores. The specific surface area SBET equals 83 m2/g and the pores volume is 0.23 cm3/g. The basic character of the surface centers of sepiolite is indicated by CO2 desorption (TPD-MS) at 170 °C and at about 620 °C due to a surface carbonates decomposition. The thermodesorption of oxygen at 650–850 °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 °C). The high-temperature reduction at about 570 °C is probably related to Ag–O–M phases on the support.The soot combustion takes place at T50 = 575 °C. Without silver (sepiolite–Zr–K–O) T50 = 560 °C but sepiolite modified with silver (sepiolite–Zr–K–Ag–O) undergoes the same process at T50 = 490 °C.