Probing the Catalytic Center of TiO2/SO4 2− Solid Superacid Catalyst by X-Band In Situ High-Temperature EPR Spectroscopy

Abstract

Paramagnetic centers of the solid superacid catalyst in the sulfated TiO 2 are prone to the electron paramagnetic resonance (EPR) spectroscopy. The induction of the catalytic-active sites in TiO 2 powder presubmerged in H 2 SO 4 solution as a function of the calcinated temperature of 293-873 K is investigated by X-band in situ continuous-wave EPR measurements. Sulfated-acid sites composed of the Ti 3? ion are formed upon calcination. The overall experimental results show that the population of these sites goes uphill with the elevating temperature, reaches a maximum at *623 K and decreases afterward to close zero. During the process, the decomposition of the TiO 2 /SO 4 2-leads to the formation of Ti 3? species and then to the increasing EPR signal amplitude, and the consecutive decomposition of the sulfur at higher temperature ([650 K) to the diminishing signal. The X-ray diffraction indicates that the introduction of SO 4 2-stabilizes the geometric structure in the anatase phase.

A potential catalyst for α-pinene isomerization: a solid superacid

“…After calcination at 600 °C and 650 °C, the crystal structures of the catalysts were completely anatase, without any rutile type. Zhang et al 26 and Zhu et al 27 showed that TiO 2 could be transformed into rutile at 600 °C without SO 4 2− . The presence of SO 4 2− will prevent this polymorphic transformation, resulting in the preservation of the anatase phase.…”

“…After calcination at 600 1C and 650 1C, the crystal structures of the catalysts were completely anatase, without any rutile type. Zhang et al 26 and Zhu et al 27 showed that TiO 2 could be transformed into rutile at 600 1C without SO 4…”

Evolution of Stable Free Radicals during Bio-Oil Pyrolysis and Its Relation to Coke Formation: An in Situ EPR Study

“…Nevertheless, most of the studies use ex situ EPR detection, which provides information on stable free radicals at the beginning and end of reactions. , Since the free radical reaction is a continuous process, the information during the reaction process could only be inferred from the initial and the final results. , The in situ EPR detection could observe the evolution of stable free radicals in real-time, reflecting the reaction process directly. In some studies of catalytic conversion of organic fuel, in situ EPR is used to measure the free radicals generated from covalent bond rupture, which has become a powerful characterization for the analysis of reaction mechanisms. − In situ EPR detection provides a new idea for studying the coke formation mechanism of bio-oil. However, limited studies use in situ EPR to study the coke formation mechanism of bio-oil, and knowledge about stable free radicals during bio-oil pyrolysis is scarce.…”