Flash pyrolysis of oil shale assisted by Zr-doped TiOSO4 nanocomposites: Excellent selectivity for hydrocarbons and toluene

Abstract

Oil shale (OS) is among the most promising alternatives to replace/complement the conventional fossil fuels of limited reserves. The manufacture of qualified petroleum-like fuels and/or value-added chemicals by a catalytic OS pyrolysis with low energy consumptions has drawn broadattention from numerous scientific and engineering communities. While the past decades have witnessed great advancements in this regard, it is still strongly desired to inaugurate new catalysts for efficient OS utilizations, since most of the currently existing catalysts either suffer from tedious pretreatments on OS, complicated fabrication, high costs, easy deactivation by pore blockage, time-consuming impregnation, or unsatisfied selectivity etc. Herein, we report that Zr-doped TiOSO4 nanocomposites could be facilely synthesized via a simple wet-chemical-calcination method. It is found that the as-fabricated nanohybrids could induce ∼10% decrements in the activation energy of OS pyrolysis, and the quality of the pyrolyzates could be greatly enhanced, where the content of heteroatomic compounds decreases from ca. 38.3% to 17.1% (55.4% reduction), that of the medium/long-chain aliphatic hydrocarbons decreases from ca. 27.7% to 17.8% (35.7% decrease), while that of hydrocarbons and short-chain aliphatic hydrocarbons increases from ca. 61.7% to 82.9% (34.4% increase) and from ca. 19.6% to 46.3% (136.2% enhancement), respectively. More significantly, our catalyst could also induce an evident increase in the content of monoaromatic hydrocarbons, especially toluene (466.7% enriched, substantially), which is an important value-added platform chemical of broad interests, and a distinct decrease in the content of polyaromatic coke precursors (36.4% reduction), which are among the most frequently encountered undesired species during OS pyrolysis. It is proposed that the synergistic yet competitive effects of Brønsted and Lewis acid sites play important roles in the excellent catalytic performances of our nanocatalyst. Considering the strategic significance of OS and the easy availability of zirconium/titanium-based nanohybrids, our nanocatalyst with excellent heteroatom removal, anti-coke and cracking capabilities, and high selectivity for hydrocarbons, short-chain aliphatic and monoaromatic hydrocarbons (especially toluene), likely initiates new opportunities for OS pyrolysis, which is a subject of broad interest and general concern.