A study on highly active Cu-Zn-Al-K catalyst for CO2 hydrogenation to methanol

Abstract

Excellent CO2 hydrogenation activity results were obtained on Cu-Zn-Al-K (CZA-K) catalyst with 10% of CO2 conversion and 98% of methanol selectivity at 220 °C. The CZA-K catalyst was precipitated by using 4 M K2CO3/KOH solution. For comparison purpose, CZA-Na and CZA catalysts were synthesized by using 4 M solutions of Na2CO3/NaOH and (NH4)2CO3/NH4OH respectively. Characterization of these catalysts was done by using BET-poresize, XRD, FTIR-DRIFTs, high pressure-TPR, CO2-TPD-mass, XPS and HAADF-STEM-EDX techniques. Among the catalysts studied maximum methanol space time yield of 14.4 mmol·gcat−·h− was obtained on CZA-K at 240 °C with 2400 h− GHSV of CO2/H2 mole ratio equals to 1:4. Greater methanol yield was associated with superior surface Cu+/Cu0 content in CZA-K was obtained through K2CO3/KOH precipitation. Further, FTIR-DRIFTs spectra suggests the interaction of CO2 with the potassium existed in the CZA framework (0.65% K, EDX) led to the formation of KO(CO)O surface species. To some extent, CO2 dissociation to CO and subsequent CH4 formation was limited by this species in presence of H2. At 240 °C, steady catalytic activity was observed for 100 h of continuous operation on CZA-K. It was associated with fewer carbon deposits formation and segregated active metals in CZA-K catalyst. The decreasing order of CO2 hydrogenation activity at 240 °C with 3.0 MPa feed-gas pressure as follows: CZA-K (14% CO2 conversion and 96% methanol selectivity) > CZA-Na (11% and 94%) > CZA (9% and 92%).