Self-assembly template combustion synthesis of a core–shell CuO@TiO2–Al2O3 hierarchical structure as an oxygen carrier for the chemical-looping processes

Abstract

Chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) are the most promising technologies for capture of CO2 at a low cost. CLC and CLOU involve cyclic reduction and oxidation of a solid oxygen carrier (OC) to transfer active oxygen from air to carbon-based fuels for combustion with the inherent feature of isolating CO2. One key issue with these technologies is to manufacture a high-performance, economical and practical OC material. In this paper, we propose a self-assembly template combustion synthesis (SATCS) method for preparing a hierarchical structure copper-based OC, Cu-rich, Al2O3-supported and TiO2-stabilized in a core–shell microarchitecture. The selection of raw materials and the rational design of OCs are based on the density functional theory (DFT) calculations and the classical Derjaguin–Landau–Verwey-Overbeek (DLVO) theory, respectively. The spontaneous aggregation between α-Al2O3 microparticles (μm-Al2O3) and rutile TiO2 nanoparticles (nm-TiO2) is driven by the van der Waals attractive and electrostatic attractive forces to form core(Al2O3)–shell(TiO2) hard templates in the wet precursor containing copper nitrate and urea. Upon calcination of the dried precursor in air, fewer nitrogen oxides (NOx) are released, demonstrating an environment-friendly fabrication process, whereby a highly dispersed and high-loading Cu-based crystalline layer is deposited on the nanostructured shell. A representative CuO@TiO2–Al2O3 OC (17.5wt% Al2O3, 5wt% TiO2) possesses hierarchical porosity and an interconnected framework and exhibits excellent performance of the reactivity, stability, oxygen release/uptake capacity and mechanical strength in the high-temperature redox cycles. The proper addition of TiO2 nanoparticles is effective in preventing the formation of copper aluminates (CuAl2O4 and CuAlO2) and inhibiting the sintering of active component grain. In addition, the rational design method and novel synthesis technique allow a mass production of various metal oxide composites used for chemical looping processes with CO2 capture and clean utilization of energy.