Sustainable CO₂ Reduction on In₂O₃ with Exclusive CO Selectivity: Catalysis and In Situ Valence Band Photoelectron Spectral Investigations

Abstract

This study demonstrates a sustainable catalytic CO2 conversion to near 100% CO selectivity at ambient pressure on In2O3. Critically, high CO yield could be observed at the cost of undesired methanation, using a lower than stoichiometric amount of hydrogen in the feed; 1:1 and 1:0.67 CO2:H2 ratios exhibit 98–99.6% CO selectivity with 25–38% CO2 conversion between 773 and 873 K. CO2 and H2 conversion under steady-state conditions at 773–873 K suggests a 1:1 ratio of adsorbed reactants (with 1:0.67 CO2:H2 feed) on the catalyst surface, underscoring the presence of an ideal reactant composition for the reverse water-gas shift reaction, while H2-rich feed compositions show the H2-dominated surface. Surface electronic structure changes, under near-operating conditions, were explored with near ambient pressure photoelectron spectroscopy (NAPPES), and the interesting findings are as follows: (a) A shift in the valence band to lower binding energy, up to 0.6 eV, was observed because of electron filling at high temperatures. (b) An observation of heterogeneous nature of the catalyst surface under NAPPES measurement conditions is attributed to the generation of active oxygen vacancy (Ov) sites, which in turn changes the work function of In2O3. (c) The above changes are found to be reversible, when the reaction was stopped. Vibrational features of the reactant molecules were observed to be broadened in the active temperature window of the catalyst supporting the heterogeneous character of the catalyst surface because of dynamic Ov generation. By optimizing gas hourly space velocity, CO2:H2 ratio, and reaction temperature, exclusive CO selectivity is possible with a H2:CO2 ratio of ∼0.67, which will avoid the product separation stage altogether, while minimizing the expensive H2 in the reactant feed.

Elucidating CO2 Hydrogenation over In2O3 Nanoparticles using Operando UV/Vis and Impedance Spectroscopies

“…This is further supported by the IR gas-phase measurements, which show the presence of hydrogen-containing adsorbates on the surface after H 2 treatment (see Figure 2). In this context, in a previous near-ambient-pressure (NAP) UPS study on In 2 O 3 during rWGSR, it was shown that the temperature as well as the CO 2 :H 2 ratio have a strong influence on the valence region, [48] which is reflected in line broadening. This is in agreement with our findings that the surface is strongly influenced by the gas environment, where a greater CO 2 content leads to greater changes, which indicates the presence of carbonaceous adsorbates.…”

Ni–Co Bimetallic Hydroxide Nanosheet Arrays Anchored on Graphene for Adsorption‐Induced Enhanced Photocatalytic CO2 Reduction

“…Furthermore, severe electron/hole recombination and slow surface reaction kinetics limit the photocatalytic performance. [5,6] Therefore, the focus of the current research is to design materials that can reduce the activation energy required for reduction reactions, increase the amount of photogenerated electrons, and accelerate the separation of electrons and holes to improve CO 2 reduction efficiency and product selectivity. [7,8] Among the developed photocatalysts, transition metal hydroxides, as noble-metal-free cocatalysts, are attractive because they are naturally abundant, cost effective, and have high CO 2 adsorption capacity.…”

Metal Ce-Leaching Induced Structural Optimization of Bismuth Electrocatalyst for Enhanced CO2 Electroreduction

“…The Ce 3d spectrum consists of two multilayer states, which correspond to spin–orbit split Ce 3d 5/2 and Ce 3d 3/2 core holes. In the O 1s spectrum, three characteristic peaks are lattice oxygen (O l , 529.7 eV), carbon–oxygen bonds (C–O, 531.2 eV), and hydroxyl oxygen (O–H, 532.3 eV), respectively (Figure g). − The similar characteristic peaks of Bi 4f, Ce 3d, and O 1s spectra can be observed in the control CeO 2 and Bi 2 O 3 samples (Figures S10 and S11). Thus, all of the above experimental results confirm the successful synthesis of CeO 2 , Ce-doped Bi 2 O 3 , and Bi 2 O 3 samples.…”