Superacidic Catalyst Containing Phosphotungstic Acid Covalently Embedded Into Silica Matrix

Abstract

Homogeneous acidic catalysts of many industrial processes cause a multitude of problems such as production of toxic waste, hazards to workers, and corrosion of expensive equipment. These problems can be avoided by heterogenization of catalytically active compounds on a solid support. The objective of this research is to synthesize a superacidic stable heterogeneous catalyst containing covalently immobilized phosphotungstic acid (PTA), and evaluate its catalytic activity. The catalyst was prepared via the sol-gel method by co-condensation of PTA with tetraethoxysilane in acidic media in the presense of surfactant Pluronic P123. Then the catalyst was granulated with aluminum oxide to prevent caking of the powder during reaction. The catalyst was mesoporous with PTA contents of 0.027 mmol/g. Its catalytic activity was tested in a fixed bed flow reactor. The catalyst demonstrated good catalytic activity in isomerization of alkenes, however, activity in alkylation of benzene was somewhat lower. In all alkylation experiments, mixtures of isomeric alkylbenzenes were obtained with 2-substituted isomer as a main product. Characterization of the catalyst after the reaction showed little changes in porosity and particle size. No leaching of PTA was observed. However, carbon deposits were found on the catalyst that requires regeneration before next use in catalysis.

Article Highlights

• Phosphotungstic acid was covalently immobilized on mesoporous silica gel;

• Obtained catalyst was successfully tested in acid-catalyzed reactions;

• No leaching of catalytically active phase was observed during the reactions.