Green sucrose-sol-gel combustion synthesis of a CuO-based oxygen carrier for NOx emission reduction and its cyclic reaction performance

Abstract

Chemical-looping combustion has attracted considerable attention as a novel combustion technology. In this study, precursors were prepared using the sol–gel method with sucrose complexation followed by combustion to synthesize CuO-based oxygen carriers (OCs) supported on an Al₂O₃–TiO₂ template. The sucrose complexing agent inhibited the release of NO_x during combustion. When the molar ratio of sucrose to Cu(NO₃)₂·3H₂O (R) was <0.36, the NO_x produced included both NO and NO₂. When R exceeded 0.73, the NO_x produced by precursor combustion was primarily NO, and its concentration was greatly reduced. A slower heating rate also reduced the release of NO_x. At a heating rate of 1 °C/min, the release of NO_x was 80% lower than that at a heating rate of 10 °C/min. All OCs were stable for ten redox cycles. Increasing the sucrose complexant content resulted in an initial increase in the reactivity of the OCs followed by a decrease. The best performing OC had an R value of 0.36 and yielded the highest mean CO₂ percentage (61.27%). When R exceeded 1.00, the sintering and agglomeration of CuO-based OCs were severe, and the mean CO₂ yield was reduced to 57.20%. The carbon deposits from the CH₄ decomposition were completely oxidized to CO₂ by the air in the reactor.