Visible light promoted low temperature photothermal CO2 methanation over morphologically engineered Ni/TiO2 NWs catalyst

Abstract

Mankind is currently faced with two ongoing major issues, namely the energy crisis and climate change. This is due to the growing human population, causing a steep increase in energy demand which is usually catered via the combustion of depleting fossil fuels. In accordance with the Sustainable Development Goals (SDGs), the utilization of carbon dioxide greenhouse gas to produce green methane fuels is deemed to be a promising approach to tackle both the aforementioned issues. Here, we successfully engineered the morphology of 3D TiO2 microparticles (TiO2 MPs) into wire-like 1D TiO2 nanowires (TiO2 NWs) via a facile solvothermal method. The nickel dispersed Ni/TiO2 NWs catalyst was then compared with its microparticle counterpart for visible light promoted low temperature photothermal CO2 methanation. Various characterization methods were conducted such as BET, BJH, FE-SEM, EDX, HR-TEM, XRD, UV–vis DRS and H2-TPR to investigate the physical and chemical properties of the catalyst samples. Initial temperature screening (150 to 300 °C) under dark and visible light irradiated conditions revealed that photothermal CO2 hydrogenation was not feasible below 250 °C. Nevertheless, the promotional effect of visible light was diminished at elevated temperatures. It was observed that the structurally modified 1D TiO2 NWs yielded a higher production rate (19.8 mmol gcat-1h−1) and selectivity (84 %) as compared to its 3D microparticle counterpart. This is mainly due to the 1D wire like structure which possesses a high surface area which increased the exposed area to visible light irradiations while promoting the dispersion of Ni active metals while limiting the growth of NiO particles. The porosity and wire like structure of 10Ni/TiO2 NWs also promoted an intimate contact between catalyst and reactants, in turn showing a prolonged durability up to 4 reaction cycles. Interestingly, the methanation performance over the 1D catalyst gradually improved over time, suggesting the visible light assisted photoreduction of NiO to metallic Ni. Thus, our findings elucidated the significance of catalyst support morphology on the photothermal driven CO2 methanation reaction.