Functionalized rice husk ash as a potential catalytic monolith: preparation, optimization and application

Rice husk ash, an undervalued resource has a vast potential for the production of innovative materials. This research focuses on its twofold exploitation to a benign cum cost-effective catalytic material and silica, thereby paving a greener approach in the context of waste utilization. In the present study, engineered ash was prepared by activating rice husk ash. The engineered ash was functionalized via sulfonation and the efficacy of the developed catalyst was evaluated through esterification of hexadecanol. An experimental matrix was generated to investigate the effect of various process parameters onto the developed catalyst and determine the optimal conditions employing response surface methodology. An optimal value of temperature 189.3 °C, time 12 h and acid char ratio 5:1 was suggested for devising a high-performance catalyst having conversion and yield of 85.72% and 44.25% with a desirability of 0.994. Finally, the optimal catalyst was overlaid onto ceramic substrates to develop monoliths and explored for its efficacy as a stirrer in the esterification of hexadecanol. The developed catalyst can be used till five cycles revealing the strong adherence of the sulfonic groups. The physicochemical properties, textural characteristics and surface morphology of optimized catalyst were characterized by Fourier-transform infrared spectra, X-ray diffraction, field emission scanning electron microscope, X-ray fluorescence and thermogravimetric analysis. A consistent performance of engineered monoliths up to five cycles makes it one of the plausible alternatives to conventional catalysts at the industrial level. Simultaneously, silica of 84% yield with 96% purity extracted from rice husk ash embraces the concept of waste valorization.