A novel mesoporous oxidation catalyst La-Co-Zr-O prepared by using nonionic and cationic surfactants as co-templates

Abstract

The mesoporous La-Co-Zr-O catalyst with the atomic ratio of La + Co/La + Co + Zr = 0.5 was prepared by citric acid complexation-organic template decomposition method, using the mixture of nonionic p-octyl polyethylene glycol phenyl ether (OP) and cationic cetyltrimethyl-ammonium bromide (CTAB) as co-templates (LCZ-OP/CTAB-0.5). The results of BET and pore size distribution show that this sample possesses much bigger specific surface area (117.6 m 2/g) than those prepared by using single template CTAB (96.6 m 2/g, LCZ-CTAB) or by using conventional co-precipitation method (21.6 m 2/g, LCZ-CO). Both the samples obtained from single template CTAB and from the co-templates of OP and CTAB show very uniform mesoporous pore diameter (3.5–4.3 nm). The structural characterization results of XRD, XPS and Co K-edge EXAFS indicate that the highly dispersed Co 3O 4 crystallite should be the main active phase for CO oxidation. The crystal sizes of Co 3O 4 crystallites in LCZ-CTAB and LCZ-OP/CTAB-0.5 are 23.4 and 32.5 nm, respectively, which are much smaller than that in LCZ-CO (56.8 nm). The catalytic activity evaluation shows that the sample prepared by co-templates decomposition possesses much better activity for CO oxidation, especially the low temperature oxidation activity. However, the activity sequence of the samples is not the same as the crystal size of Co 3O 4 phase. On the contrary, the reducibility of bond Co–O and the reduced amount of Co 3O 4 phase below 500 °C for the samples are well correlated with their activity law, which should be a crucial factor for the oxidation performance of the samples.