Reaction between Thiophene and Ni Nanoparticles Supported on SiO2or ZnO: In Situ Synchrotron X-ray Diffraction Study

Abstract

Synchrotron X-ray powder diffraction (XRD) and mass spectrometry were applied in situ to study the interaction of thiophene with Ni0 particles (5−6 nm) deposited on inert (SiO2) or sulfidable (ZnO) supports. The reaction was performed in a hydrogen flow containing 20−40 mbar of thiophene at 280−360 °C for Ni/SiO2 and at 360 °C for Ni/ZnO. Surprisingly, in the first XRD pattern of the solid recorded after introduction of thiophene in the reactor, we observed a considerable increase of the Ni cell parameter: Δa = 0.06 Å for Ni/SiO2 and Δa = 0.15 Å for Ni/ZnO at 360 °C. The simultaneous presence of CH4 in the gas phase revealed that in this stage thiophene molecules undergo complete hydrogenolysis. During this reaction, carbon adatoms can also be produced and their diffusion into the bulk of Ni nanoparticles was supposed to provoke the observed lattice expansion. After this initial stage, the SiO2-supported Ni nanoparticles transformed progressively into a complex mixture of phases with the composition dependent on the reaction temperature: at 280 °C the main product was identified as Ni3S2 (cubic modification and heazelwoodite), while at 360 °C it was Ni3C. The behavior of ZnO-supported Ni is different. The carbon-modified dilated Ni nanoparticles, formed in the initial stage, remained intact until the end of ZnO sulfidation to be later transformed into Ni3C. On the basis of these results, we concluded that carbon-modified Ni particles play the role of an active phase during the reactive adsorption of thiophene on Ni/ZnO.