Catalytic Activity of the H2O/CO2 System in Lignocellulosic-Material Decomposition

Water coordinated on Cu(I)-based catalysts is the oxygen source in CO2 reduction to CO

Catalytic reduction of CO₂ over Cu-based catalysts can produce various carbon-based products such as the critical intermediate CO, yet significant challenges remain in shedding light on the underlying mechanisms. Here, we develop a modified triple-stage quadrupole mass spectrometer to monitor the reduction of CO₂ to CO in the gas phase online. Our experimental observations reveal that the coordinated H₂O on Cu(I)-based catalysts promotes CO₂ adsorption and reduction to CO, and the resulting efficiencies are two orders of magnitude higher than those without H₂O. Isotope-labeling studies render compelling evidence that the O atom in produced CO originates from the coordinated H₂O on catalysts, rather than CO₂ itself. Combining experimental observations and computational calculations with density functional theory, we propose a detailed reaction mechanism of CO₂ reduction to CO over Cu(I)-based catalysts with coordinated H₂O. This study offers an effective method to reveal the vital roles of H₂O in promoting metal catalysts to CO₂ reduction.

Understanding the underlying mechanisms for catalytic reduction of CO₂ over Cu based catalysts remains challenging. Here, the authors develop an effective method to reveal the vital roles of H₂O in promoting metal catalysts to CO₂ reduction via a modified triple stage quadrupole mass spectrometer.

Hydrolysis of Lignocellulosic Biomass in Hot-Compressed Water with Supercritical Carbon Dioxide

This study investigated the decomposition behavior of bamboo under hydrothermal and hydrolysis conditions with H2O/CO2 in a semicontinuous-flow reactor at 9.8 MPa. At 255 °C, with and without CO2, xylan in bamboo completely decomposed into xylo-oligosaccharide (XOD). The yield of glucan degradation products with CO2 was significantly higher compared with that under the hydrothermal reaction (25.7 vs 14.9 wt %, respectively). The reaction rate of glucan decomposition with CO2 was slightly higher than the rate of hydrothermal reaction (k H2O/CO2 /k H2O = 1.3). Increasing the fluid velocity of the hydrothermal reaction (3-10 mL/min) significantly accelerated the solubilization rate, but the ultimate yield of the soluble fraction was unchanged. The ultimate yield of the soluble fraction was slightly affected by physical effects. Hydrolysis with CO2 under severe conditions exhibited effective degradation of glucan. The catalytic activity of the H2O/CO2 system under hydrolysis can be explained by the system's chemical effect.