۱- Introduction

۲- Experimental

۳- Results and discussion

۴- Conclusions

References

Abstract

Here, we report the preparation of a Cr/ZrO2 composite catalyst for the reverse water-gas shift reaction (RWGS) that shows excellent low-temperature CO2 conversion and 100% CO selectivity. The catalyst was prepared from Cr-containing wastewater by photoreduction. Zirconia was used as a wide bandgap photocatalyst to photoreduce Cr(VI) under UV irradiation and immobilize the Cr species on the catalyst surface, resulting in a high dispersion. The results show that the obtained 1 wt%Cr/ZrO2 can catalyze the RWGS to reach the thermodynamic limit at 600 °C. The CO yield at 600 °C with photoreduced Cr/ZrO2 after calcination, 38.34%, is significantly higher than that of the catalyst prepared by impregnation. Metal hydrides were determined to be the key intermediates in the RWGS reaction with Cr/ZrO2 as the catalyst, and the cyclic conversion between Cr(VI) and Cr(III) caused by the hydrogen reduction and CO2 oxidation improves the catalytic activity. This study provides a strategy to acquire a promising RWGS catalyst for CO2 emission reduction and utilization and an attractive method to treat Cr-containing wastewater.

Introduction

Carbon dioxide hydrogenation is an effective strategy for CO2 emission reduction and utilization[1], and the reverse water-gas shift reaction (RWGS) is an attractive and promising route[2] for this process with industrial value. CO2 is typically inert but can be activated and converted into valuable CO with low hydrogen consumption in the RWGS. The CO can be used for further production with value-added products such as methanol[3] in the CAMERE (Carbon Dioxide Hydrogenation to Form Methanol via a Reverse-Water-Gas-Shift Reaction) process and alkenes[4] in alkane oxidative dehydrogenation. As a typical endothermic reaction, the RWGS reaction enthalpy is 42.1 kJ mol-1 . Thus, the most favorable reaction conditions involve high temperatures and a high ratio of hydrogen to CO2 for reaction conversion enhancement. However, the high reaction temperatures result in high energy consumption and rapid catalyst deactivation because of severe carbon deposition, as well as competitive methanation side reactions. A high hydrogen-to-carbon ratio increases the operating costs and makes it difficult to adjust the proper hydrogen-carbon ratio for follow-up production. Thus, the development of a catalyst with excellent low-temperature activity and good anti-coking capability with a low hydrogen-to-carbon ratio for the RWGS was investigated.