Catalytic activities of Fe2O3 and chromium doped Fe2O3 for sulfuric acid decomposition reaction in an integrated boiler, preheater, and catalytic decomposer

Abstract

In our earlier work (Banerjee et al. [29]) we have reported the catalytic properties of powders of Fe2(1−x)Cr2xO3 (x=0.0, 0.1, 0.2) for sulfuric acid decomposition in a flow through quartz catalytic reactor with 2g catalyst in presence of nitrogen as a carrier gas. With a practical application approach, in this work the two screened oxides, iron oxide and 10% chromium doped iron oxide, that showed good initial promise as catalyst for sulfuric acid decomposition were prepared in granular form and evaluated for sulfuric acid decomposition reaction using an indigenously developed dual tube quartz reactor which served as an integrated acid boiler, pre-heater, and decomposer. The effect of reaction variables, e.g., temperature, time, and acid flow rate on the catalytic activity was evaluated in detail employing 20g of granular catalyst and 98wt% H2SO4 (without any carrier/diluents gas). Temperature dependent catalytic activity results revealed that at lower temperatures (<775°C) the Cr-doped sample showed much higher activity while at higher temperatures (∼825°C) the conversions levels were found to be similar on both the samples. No decrease in catalytic activity was observed for either catalysts during a 100h catalytic run at 800°C and at an acid flux of ∼0.63mlmin−1, but the chromium doped sample exhibited slightly higher activity over the entire time period. Both the catalyst exhibited a loss in catalytic activity when subjected to higher flow rates of sulfuric acid in the range 2–10mlmin−1. The catalytic activities were correlated with the structure, morphology, redox, and thermal properties of the oxides by proper characterization of the fresh and the spent catalysts by XRD, FTIR, XPS, TPR, evolved gas analysis, and SEM. From the ex situ analysis of the spent catalyst samples the most probable mechanism of the high temperature sulfuric acid decomposition reaction was also proposed, which involves metal sulfate formation and decomposition steps. The enhanced catalytic activity of Cr-doped Fe2O3 was ascribed to lower thermal stability of its sulfate and better redox properties.