Applied Catalysis B: Environmental, Vol.241, 217-226, 2019
Improving low-temperature CS2 conversion for the Claus process by using La (III)-doped nanofibrous TiO2 xerogel
Not only do the natural gas and petroleum industries face the challenge of stringent sulfur compound emission limits, but it is also important to use new technologies to reduce the carbon footprint and improve energy efficiency. Herein this research is aimed at developing a new generation of catalysts that can potentially decrease the reaction temperature of Claus catalytic converters (used to convert sulfur compounds to elemental sulfur), and also reduce the amount of catalyst. There are two factors that affect the performance of the conventional Claus catalysts. First, the conventional metal oxide catalysts suffer from ageing, trapped liquid sulfur fouling in the mesopores and high steady-state concentration of surface sulfate, which reduce the number of active sites for CS2 conversion. Therefore, the industry has to pay the price for a high reaction temperature to maintain a satisfactory CS2 conversion, while sacrificing Claus conversion (2H(2)S + SO2). Second, Al2O3 and TiO2 are widely used for Claus reactions; nevertheless, they are not active for conversion of CS2 at lower temperatures. In this context, our approach in this research is using nanofibrous La(III)-doped TiO2 as a new Claus catalyst. La(III) is incorporated into titanium-oxo-acetate complexes via a one-pot sol-gel process, followed by calcination to form a nanofibrous xerogel. Because the nanofibers join together to form a connected network, the xerogel monolith has large macroporosity and exhibits a low density. The exterior surface of the nanofibers, which makes a large contribution to the surface area, remains intact under harsh conditions and thereby is accessible by the reactants. In addition, the La(III) doped TiO2 exhibits more Lewis-base activity that is effective for CS2 conversion. For comparison, TiO2 xerogels were deposited with La(III) by means of an impregnation method and also tested for Claus reaction activity; however, the catalytic performance of this material was reduced compared to the pure TiO2 counterpart. On the basis of characterization studies on these catalysts, it is concluded that (i) a good distribution of La(III) in TiO2 matrix and (ii) the method of La(III) incorporation are important for CS2 conversion.