Structural and composition enhancement of Indian Kachchh kaolin clay: characterisation and application as low-cost catalyst

Abstract

ABSTRACT The effect of acid treatment on kaolin clay from the Kachchh region of Gujarat, India, was explored to prepare a low-cost (−$0.6/kg) catalyst. The clay was treated with 10 M H2SO4 which increased the Si/Al ratio from 1.3 to 2.4, surface area from 10.322 to 54.193 m2/g and pore volume from 0.041 to 0.152 cm3/g. The XRF analysis indicated that the metal oxides in treated clay decreased with increasing acid strength; consequently increasing the SiO2 content. SEM micrographs displayed gradual disaggregation and decrease in the size of clay structure with an increase in acid strength. TG-DTA study confirmed the removal of structural water. FTIR and X-ray diffraction analysis indicated metal removal creating a large degree of structural disorder resulting in reduced crystallinity and leading towards the amorphous phase. BET study confirmed the formation of additional mesopores. The acid-treated clay was applied as a catalyst for the esterification of succinic acid (SA) with ethanol. The conversion of SA increased from 27% to 56% revealing higher activity and selectivity in terms of higher yield (96%) of valuable diester. The catalyst was reused up to three cycles with a slight loss of catalytic activity. GRAPHICAL ABSTRACT