CHARACTERISATION AND ACTIVITY OF Cu-Zn-Al-Zr/ZSM-5 HYBRID CATALYSTS FOR CO2 HYDROGENATION REACTION: EFFECT OF THE IMPROVISED PREPARATION TECHNIQUE

Abstract

An improvised preparation technique, namely ultrasonic spray precipitation (USP) was employed in preparing Cu-Zn-Al-Zr/ZSM-5 zeolite hybrid catalysts. The effects of the newly improvised technique on the physicochemical properties as well as the catalytic behavior of CO₂ hydrogenation reaction were studied. This technique exploits the capability of spraying effect in generating micro-droplets upon contact of catalyst precursors with precipitating agent and also the introduction of an ultrasonic energy in assisting the precipitation process. The characterisation data showed that the USP technique dictates the formation of ultrafine crystallite size (75–99 nm) as compared to conventional technique (CP). The addition of ZSM-5 zeolite had influenced the BET surface area and acidity characteristic (NH₃-TPD) of the catalysts regardless of the preparation method employed. Reducibility analysis (H₂-TPR) revealed that the USP catalysts can be easily reduced at low temperature range of 467–469 K and the existence of single reduction peak explains good interactions between different elements in the catalyst with the formation of single form of oxide species. Moreover, this study also showed that catalysts prepared by USP technique absorbed higher H₂ as compared to their respective CP-prepared catalysts. This trend was also in line with CO₂ conversion data in which Cu-Zn-Al-Zr/ZSM-5 zeolite hybrid catalyst recorded the highest conversion at 55.4 % (503 K, 30 bar, 10,000 h^-1 GHSV).