Energy-efficient CO2 hydrogenation with fast response using photoexcitation of CO2 adsorbed on metal catalysts.

Many heterogeneous catalytic reactions occur at high temperatures, which may cause large energy costs, poor safety, and thermal degradation of catalysts. Here, we propose a light-assisted surface reaction, which catalyze the surface reaction using both light and heat as an energy source. Conventional metal catalysts such as ruthenium, rhodium, platinum, nickel, and copper were tested for CO2 hydrogenation, and ruthenium showed the most distinct change upon light irradiation. CO2 was strongly adsorbed onto ruthenium surface, forming hybrid orbitals. The band gap energy was reduced significantly upon hybridization, enhancing CO2 dissociation. The light-assisted CO2 hydrogenation used only 37% of the total energy with which the CO2 hydrogenation occurred using only thermal energy. The CO2 conversion could be turned on and off completely with a response time of only 3 min, whereas conventional thermal reaction required hours. These unique features can be potentially used for on-demand fuel production with minimal energy input.

Computational prediction of high methane storage capacity in V-MOF-74.

The methane adsorption properties in M-MOF-74 (M = Mg, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn) were investigated for potential adsorbed natural gas (ANG) vehicle applications. In particular, density functional theory (DFT) simulations were conducted to derive the force field parameters that were used in the grand canonical Monte Carlo (GCMC) simulations to obtain the methane adsorption isotherm curves. Our results indicate that commonly used DFT exchange correlation functionals (e.g. vdW-DF, vdW-DF2, PBE+D2) overestimated the methane binding strength to the metal sites, leading to inaccurate description of the adsorption properties. As such, the global scaling factor within the exchange correlation functional, PBE+D2, was optimized to find a suitable functional that leads to good agreement with the available experimental methane adsorption data. From the newly derived force field parameters, our computational simulations predict a methane uptake of 279 cm3 cm-3 in V-MOF-74 at T = 298 K and P = 65 bar (condition relevant to ANG storage operation), which would be higher than the current record holder of HKUST-1 (270 cm3 cm-3). Although the methane working capacity (65-5.8 bar uptake difference) is low due to strong binding of methane with the V-MOF-74, varying the process conditions (e.g. lower adsorption temperature, higher desorption temperature, lower desorption pressure) can lead to a significantly high methane working capacity, towards the goal of meeting the DOE requirements for ANG technology.