Cordierite/steatite/CeO2 porous materials – Preparation, structural characterization and their photocatalytic activity

Abstract

The study is focused on structural characterization of new cordierite/steatite/CeO2 ceramic catalysts sintered from the mixtures containing vermiculite/CeO2 (Ver/CeO2) ceria precursor and testing their photocatalytic ability to decompose nitrous oxide (N2O). Two preceramic mixtures named A and B contained the amount of kaolinite (47 wt% and 50 wt%, respectively), different quantity of talc (40 wt% and 20 wt%, respectively) and vermiculite (13 and 30 wt%, respectively). Their counterpart mixtures A/CeO2 and B/CeO2 contained vermiculite/CeO2 instead of pure vermiculite. Ceramic cordierite/steatite (A and B) and cordierite/steatite/CeO2 (A/CeO2 and B/CeO2) sintered at 1300 °C were composed of indialite, hexagonal form of cordierite, orthorhombic protoenstatite and orthoenstatite, and CeO2 (3 wt% at A/CeO2 and 10 wt% at B/CeO2). The cordierite/steatite ceramic samples A and B showed the porosity 34 and 21%, respectively, a unimodal pore size distribution and the median pore diameter 22 and 15 μm, respectively. The cordierite/steatite/CeO2 samples A/CeO2 and B/CeO2 showed bimodal pore size distribution and porosity of 54 and 58%, respectively, and the median pore diameter 8 and 7 μm, respectively. A mean crystallite size D(220) of CeO2 was found for Ver/CeO2 = 8.5 ± 0.5 nm, A/CeO2 = 27.1 ± 2.8 nm and for B/CeO2 = 31.1 ± 3.0 nm. Photocatalytic decomposition of N2O over the ceramic samples A/CeO2 and B/CeO2 was performed during 20 h in annular batch reactor illuminated with 8 W Hg lamp (254 nm wavelength). Reaction kinetic corresponds to first-order reaction rate which is in agreement with plausible reaction mechanisms. The highest N2O conversion of 91% was achieved over the sample B/CeO2.