Catalytic function of Y2O3-based catalyst in chemical looping synthesis of C2H2 from inorganic C and H2O at moderate temperatures

Chemical looping technology offers promising opportunities for converting CO 2 /H 2 O to high value-added products (e.g., CO, H 2 , and C 2 H 2 ) by using well designed metal oxides as oxygen carriers. Herein, the calcium oxide (CaO) was used as oxygen carrier to synthesize acetylene (C 2 H 2 ) from inorganic carbon material (e.g., active carbon (AC)) and H 2 O via chemical looping route, which is constituted by two basic steps: solid-phase synthesis of calcium carbide (CaC 2 ) (redox reaction) and C 2 H 2 production (metathesis reaction). To further enhance the energy utilization efficiency of this chemical looping process, transition metal oxides (ZrO 2 , La 2 O 3 , and Y 2 O 3 )-based catalysts were used to promote the solid-phase redox reaction between CaO and carbon reactants. Compared with blank test, 5 wt% cubic Y 2 O 3 as a catalyst that added into CaO-AC mixture can further increase the CaO conversion by ∼40% under optimal conditions and the onset solid-phase reaction temperature between CaO and AC decreases to ∼1620 °C. This catalytic effect is ascribed to the enhanced chemical reaction at the solid–solid interface of CaO and AC reactants and promoted ionic conductivity (e.g., Ca 2+ , O 2– conduction) of the bulk after adding Y 2 O 3 catalyst, leading to a decreased average apparent activation energy ( E a ) (∼909 kJ mol −1 ) of CaC 2 formation. Our work demonstrates that constructing of catalytic solid-phase reaction system by adding selected transition metal oxides as catalysts can effectively reduce the E a of solid-phase CaC 2 synthesis and enhance the overall efficiency of chemical looping synthesis of C 2 H 2 , which sheds light to synthesize organic compounds from inorganic materials in large scale.