A size-selective method for increasing the performance of Pt supported on tungstated zirconia catalysts for alkane isomerization: a combined experimental and theoretical DFT study

Abstract

The trends in the development of acid catalysts for isomerization show that the diffusion and accessibility of products are more favored in mesoporous as compared to microporous materials. In this work, an easy metal alkoxide- and surfactant-free technique was developed to prepare mesoporous size-selective Pt/WO₃–ZrO₂ catalysts. A high-octane number blend was obtained in the nC₆ isomerization reaction with these catalysts. The use of H₂O₂ produced an increase in the textural properties of the tungstated zirconia that generated a high expulsion of tungsten, significantly benefitting the development of Brønsted acid sites required in alkane isomerization reactions. Results show that these catalysts reached high conversion values (up to 85 mol%) and higher selectivity for bi-ramified isomers as compared to conventional tungstated zirconia (17 mol% for 2,2-dimethyl-butane and 13 mol% for 2,3-dimethyl-butane). The high catalytic activity is attributed to their improved mesoporous structure that allowed the formation of well-dispersed WO_x clusters on the zirconia surface with an intermediate domain size. DFT calculations confirmed that intermediate WO_x cluster sizes offer the best balance between the strength and number of Brønsted acid sites.