Effect of metal oxide supports on active-Cu for CO/CO2 hydrogenation to methanol

Abstract

Increasing tensions over global warming, talks about a sustainable future and a huge imbalance in closure of the carbon cycle indicate a response for developing efficient conversion of CO2 and syngas obtained from renewable sources. Thermochemical conversion of carbon oxides (CO and CO2) in combination with hydrogen to produce methanol in the presence of catalyst provides a pathway to close this carbon cycle. Steady state activity tests were carried out in a small integral reactor for methanol synthesis from a mixture of either CO/H2 or CO2/H2. The temperature was varied from 200 to 300°C, while the total pressure was held constant for CO/H2 at 85 bar and CO2/H2 at 60 bar keeping stoichiometric flow of hydrogen at GHSV of 24,000 hr¡1. Four different metal oxides namely ZnO, ZrO2,MgO and CeO2 were investigated for support effects on active Cu along with different combinations among them while keeping commercial catalyst as the benchmark. Catalysts were prepared using urea hydrolysis method. It was found that ZrO2 and MgO show higher selectivity however the latter does not exhibit comparable conversion as the commercial catalyst for CO2 hydrogenation. Detailed GHSV study for Cu-ZrO2 paint a completely different picture showing higher methanol selectivity (64%) with increasing space velocity (at GHSV of 32,000 hr¡1). In case of COhydrogenation, commercial catalyst performs the best, albeit displaying signs of carbon deposition at higher temperature (280°, 300°C). This situation is circumvented by employing ZnO/MgO combination as a support. Cu-CeO2 exhibited characteristics of an excellent water gas shift catalyst. This led to a novel configuration of mixed bed consisting of Cu-CeO2 with commercial catalyst. Results indicate that this combination improves themethanol yield by atleast 30% as compared to commercial catalyst at a high GHSV of 24,000 hr¡1.