Photocatalytic Synthesis of Methacrylic Acid from CO_2 and C_3H_6 on Cu/MoO_3-TiO_2

Photocatalytic synthesis of hydrocarbon oxygenates from CO 2 and hydrocarbons is of great importance to environmental protection, utilization of carbon resources and synthetic chemistry. The adsorption property of CO 2 and C 3H 6 and the photo-stimulated surface reaction to synthesize methacrylic acid (MAA) from CO 2 and C 3H 6 on the Cu/MoO 3-TiO 2 catalyst were studied. The experimental results pointed out that there existed three kinds of active sites on the surface of Cu/MoO 3-TiO 2 catalyst: metallic site Cu, Lewis acid sites Mo 6+ and Ti 4+, Lewis base sites bridge O in Mo-O-Ti and terminal O in Mo=O. Chemisorbed CO 2 on the surface of Cu/MoO 3-TiO 2 catalyst formed high active horizontal state Cu-(CO)-O→Ti 4+(Mo 6+) by the synergic action of metallic site Cu and Lewis acid sites Ti 4+ (Mo 6+), while dual-sites adsorption of β-H and β-C of C 3H 6, which formed state Cu-C(CH 2)(CH 3)-H→ O=Mo, had been found mainly on the Lewis base site Mo=O and the metallic site Cu, respectively. The blue-shift of band edge of absorption spectra and the increase of luminous absorption capacity on Cu/MoO 3-TiO 2 catalyst improved the catalytic activity of Cu/MoO 3-TiO 2. Photo-quantum efficiency of the surface reaction of CO 2 and C 3H 6 on Cu/10%MoO 3-TiO 2 was the highest, which reached 22 8%, and the selectivity for MAA was over 95% under the proper reaction conditions (p=0 1 MPa, SV=200 h -1, T=383 K and power=125 W). Based on the experimental results, a possible mechanism was proposed for the photo-stimulated surface reaction of CO 2 and C 3H 6 to synthesize MAA on Cu/MoO 3-TiO 2 catalyst.