Rational synthesis of TS-1 zeolite to direct both particle size and framework Ti in favor of enhanced catalytic performance

Abstract

Abstract Simultaneous control over particle size and framework Ti content are the major challenges of synthesis of efficient TS-1 catalysts. Here we firstly report control over the particle size and framework Ti content of TS-1 catalysts in a wide range through conventional hydrothermal approach, evaluate catalytic performances of obtained TS-1 catalysts, and then rationally design a novel procedure of synthesis. The characterization of TS-1 catalysts by several techniques revealed that synthesis conditions through conventional hydrothermal approach to reach minimum particle size is different than that to reach maximum framework Ti content. The catalytic study of TS-1 catalysts showed that conversion of phenol (kinetic diameter of 0.57 nm) increased with increase in the particle size, reached a maximum of 29.9% for the TS-1 with particle size of 270 nm, and then dropped significantly for the TS-1 with biggest particle size. The conversion of dibenzothiophene (kinetic diameter of 0.9 nm), however, decreased with increase in the particle size and maximum conversion of 69.0% was achieved by the TS-1 with smallest particle size of 130 nm. No TS-1 catalyst synthesized through conventional approach was efficient in oxidation of the both substrates as the catalyst lacks either small particle size or enhanced framework Ti. Based on the property-function results from conventional synthesis, we rationally designed a novel synthesis of TS-1 with minimum water and optimum pH by (NH4)2CO3 addition to minimize the particle size and maximize framework Ti content, respectively. The resultant TS-1 with both features of small particle size of 185 nm and enhanced framework Ti resulted in full conversions of phenol and bulky substrate of dibenzothiophene and generates the least amount of wastewater. The new approach applied here is promising and applicable to make efficient Lewis-acid zeolites.