Mesoporous oxidic holey nanosheets from Zn-Cr LDH synthesized by soft chemical etching of Cr3+ and its application as CO2 hydrogenation catalyst

Abstract

High surface area mesoporous holey hydroxidic nanosheets were synthesized by reacting Zn-Cr-LDH with β-diketonate ligands. The different β-diketonate ligands having keto-enol tautomeric behaviour and the strength of enolic acids increasing in the order 1-phenyl-1,3-butanedione<2,4-pentanedione<1,1,1-trifloro-2,4-pentanedione were reacted with Zn-Cr-LDH. Strong 1,1,1-trifluoro-2,4-pentanedione reacted with Zn-Cr-LDH at room temperature itself and broken the layered structure of LDH forming a segregated Cr3+ stable diketo complex. On the other hand, 2,4-pentanedione and 1-phenyl-1,3-butanedione reacted with Zn-Cr-LDH at temperatures 45 and 65°C respectively. 2,4-Pentanedione preferentially etched out Cr3+ ion by leaving behind the LDH like structure with mesoporous holes. 1-Phenyl-1,3-butanedione due to its still weaker acid strength could not etch out Cr3+ ion. The pores obtained in the LDH nanosheets from the reaction with 2,4-pentanedione were found within a narrow size range of 2–10nm. Also, their BET surface area was higher. The calcined form of this mesoporous material was used as a catalyst for the hydrogenation of CO2. The catalytic reactions carried out at temperature 200–400°C showed approximately 100% selectivity towards CH4 with a small amount of H2O as a by-product without the deposition of coke and formation of additional CO. Thus, by virtue of its improved performance at lower temperatures it is expected to have an advantage over many existing similar CO2 hydrogenation catalysts.