Abstract
The performance of alumina supported unpromoted and cerium promoted nickel catalysts in CO2 methanation reaction was investigated. It was found that the activity of catalysts in CO2 methanation reaction at low reaction temperatures can be improved by the increase in nickel loading and introduction of cerium promoter. The catalysts showed high resistance for sintering and coking at high reaction temperatures. A few stages of catalysts deactivation by H2S in the methanation reaction carried out at 475 °C with the time on stream were identified. It was found that an introduction of H2S to the stream (8 ppm) did not induce rapid decrease of activity. Slight and then strong drop of CO2 conversion and simultaneously the loss of methane selectivity was observed after specific time, depending on the catalysts composition. Deactivation of catalysts was related to the nickel content and the presence of cerium. X-ray diffraction studies indicated small changes of crystallite size with the time on stream. Raman spectroscopy studies pointed out that deactivation of catalysts was not connected with formation of carbon deposits. An in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy studies showed that exposition of catalysts to the reaction mixture containing the traces of H2S led to the blocking of nickel active sites responsible for CO2 and H2 activation and successive transformation to carbonyl and formate species.
Highlights
The increase in the demand for energy carriers and chemical products in the last decades, connected with an increase in population growth and industrial development has brought significant environmental threats, including over-exploitation of natural resources, massive consumption of fossil fuels and greenhouse gas emission, unprecedented in the history of civilization [1, 2]
Alumina supported nickel catalysts, containing 20 and 40 wt% Ni were prepared by the impregnation method in the presence of citric acid
An increase in nickel content and introduction of promoter led to the increase of the active surface area
Summary
The increase in the demand for energy carriers and chemical products in the last decades, connected with an increase in population growth and industrial development has brought significant environmental threats, including over-exploitation of natural resources, massive consumption of fossil fuels and greenhouse gas emission, unprecedented in the history of civilization [1, 2]. The first concept assumes the hydrogenation of bio-CO2 without purifying the stream from sulfur compounds, but at their concentration at the level that ensures the operation of catalysts in the form of sulfides. Studies have been focused on the hydrogenation reaction of carbon monoxide, e.g. contained in the synthesis gas produced by gasification of sulfated coal. Typical representatives of this group are molybdenum based catalysts [44,45,46]. The aim of the studies was determination of the activity and durability of cerium promoted alumina supported nickel catalysts in C O2 methanation reaction in H2S free and contaminated streams
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