Using tungstophosphoric acid-modified CeO2, TiO2, and SiO2 catalysts to promote secondary reactions leading to aromatics during waste tire pyrolysis

Abstract

The synthesis of catalysts for upgrading waste tire pyrolysis oils (TPO) into marketable products such as fuels, solvents or fine chemicals is a major challenge. Herein, the effect of CeO2, SiO2, and TiO2 catalysts containing tunsgtophosphoric acid (TPA) on the selectivity to aromatics (benzene, toluene, and xylenes viz. BTXs) and p-cymene was studied for the first time. Modifying TiO2 with 1% and 10% TPA allowed modulating the oxide's acidity, resulting in a ratio of Lewis acid sites and strong Brønsted acid sites that favored the target compound formation. The 1%TPA catalyst enhanced the p-cymene production (Sp-cymene = 56.3%). In contrast, 10%TPA promoted BTX formation (SBTX= 26%) over p-cymene (Sp-cymene = 6.5%) due to its greater content of Brønsted acid sites. The selectivity of SiO2 and CeO2-based catalysts to these aromatic compounds was in the same order as the uncatalyzed reaction. The p-cymene is mainly formed from secondary reactions of isomerization of limonene to other terpenes (terpinolene, α-terpinene, and γ-terpinene) and the subsequent ring dehydrogenation with an activation energy of 62.3 kJ mol−1. The BTXs were kinetically favored on 10%TPATi catalyst with an Ea = 112 kJ mol−1. The study was performed in a fixed bed Pyr-GC/MS system under kinetically controlled regime.