Transformation of titanium carbide into mesoporous titania for catalysed HBr oxidation

Abstract

Herein, we report TiC as precursor of a highly active and novel TiO2-TiC composite for the catalytic oxidation of HBr into Br-2, which is a key technology for bromine looping in the halogen-mediated process for natural gas valorisation. In addition, we investigate the mechanism of TiO(2)formation that is pivotal in deriving synthesis-structure-performance relationships. In-depth material characterisation, by means of X-ray diffraction, thermogravimetric analysis, N(2)sorption, Raman, X-ray photoelectron,Ti-47,Ti-49 and(13)C nuclear magnetic resonance spectroscopies, as well asex situandin situtransmission electron microscopy reveal that the transformation of TiC proceedsviaa combination of shrinking core and spot-oxidation mechanisms. This results in the formation of a TiO2-TiC composite, containing both anatase and rutile polymorphs, with enhanced mesoporosity, reaching up to a one order of magnitude higher surface area and pore volume compared to pristine TiC. Reactivity and kinetics studies are performed in HBr oxidation, showing that the catalyst activity follows a volcano behaviour, whose apex is found for the material calcined at 673 K. Its performance surpasses that of benchmark TiO2-P25 and is also found stable for 25 h on stream. Accordingly, the reactivity of the TiO2-TiC composite is rationalized based on the TiO(2)generation and porosity formation, which are both functions of the oxidation temperature.