Effect of reduction pretreatment on the structure and catalytic performance of Ir-In 2 O 3 catalysts for CO 2 hydrogenation to methanol.

In ₂ O ₃ has been found a promising application in CO ₂ hydrogenation to methanol, which is beneficial to the utilization of CO ₂ . The oxygen vacancy (O _v ) site is identified as the catalytic active center of this reaction. However, there remains a great challenge to understand the relations between the state of oxygen species in In ₂ O ₃ and the catalytic performance for CO ₂ hydrogenation to methanol. In the present work, we compare the properties of multiple In ₂ O ₃ and Ir-promoted In ₂ O ₃ (Ir-In ₂ O ₃ ) catalysts with different Ir loadings and after being pretreated under different reduction temperatures. The CO ₂ conversion rate of Ir-In ₂ O ₃ is more promoted than that of pure In ₂ O ₃ . With only a small amount of Ir loading, the highly dispersed Ir species on In ₂ O ₃ increase the concentration of O _v sites and enhance the activity. By finely tuning the catalyst structure, Ir-In ₂ O ₃ with an Ir loading of 0.16 wt.% and pre-reduction treatment under 300°C exhibits the highest methanol yield of 146 mg _CH3OH /(g _cat ·hr). Characterizations of Raman, electron paramagnetic resonance, X-ray photoelectron spectroscopy, CO ₂ -temperature programmed desorption and CO ₂ -pulse adsorption for the catalysts confirm that more O _v sites can be generated under higher reduction temperature, which will induce a facile CO ₂ adsorption and desorption cycle. Higher performance for methanol production requires an adequate dynamic balance among the surface oxygen atoms and vacancies, which guides us to find more suitable conditions for catalyst pretreatment and reaction.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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