Adsorption–desorption equilibrium investigations of n-butane on nanocrystalline sulfated zirconia thin films

Abstract

Nanocrystalline thin films of the alkane skeletal isomerisation catalyst sulfated zirconia were successfully deposited on a silicon substrate in order to allow the application of surface science techniques. Thermal treatment of the films was optimised to chemically mimic the powder preparation process, resulting in films possessing the essential features (including tetragonal phase, nanocrystallinity and sulfur content of ~3 atomic %) of active powder catalysts. The n-butane adsorption-desorption equilibrium under isobaric conditions (10 -8 to 10 -6 hPa) over the temperature range 300-100 K was monitored by photoelectron spectroscopy. Analysis of the isobars revealed strong and weak n-butane chemisorption sites, releasing heats of between 59-40 and 47-34 kJ/mol, corresponding to 5 and 25% of a monolayer coverage, respectively. The total amount of chemisorbed n-butane coincides with the estimated number of surface sulfate groups. An increase in adsorption heat was observed between coverages of ~5-8% of a monolayer, indicating adsorbate-adsorbate interactions. It follows that adjacent sites are present and isomerisation by a bimolecular surface reaction is feasible. Physisorption on the films generates heats of ~28 kJ/mol, for coverages from 30% up to a complete monolayer. Multilayer adsorption results in the formation of an electrically insulating adsorbate structure. It is proposed that the strong chemisorption sites correspond to an interaction with a minority disulfate species.

In‐situ characterization of aqueous‐based hafnium oxide hydroxide sulfate thin films

“…The S 2p spectra were fit with a spin‐orbit‐split doublet (1.2 eV) and a constant FWHM (1.85 eV) for all annealing conditions. The main change in the S 2p spectra was a shift to slightly higher binding energy from 168.4 eV at RT to 168.9 eV at 750 K. In all cases, these values are consistent with sulfate species and not a conversion to sulfite or other sulfur oxidation state upon annealing . The O 1s spectra are the most complex from these samples, and several different methods were examined to fit the data.…”

Sulfated Zirconia Synthesized in a One Step Solvent-Free Method for Removal of Olefins from Aromatics

“…Meanwhile, the composition in sulfated zirconia is not simply full of Zr­(SO 4 ) 2 . Mass fraction of S in the sulfated zirconia is about 3.5% instead of 22.6% in zirconium sulfate. , The unsolved problem of acidic properties is related to its special structure and connection mode between S and Zr atoms. , Then S coverage (× 10 –6 mol S·m –2 ) on the surface of ZrO 2 and its impact in acidic sites are fundamental problems in revealing acidic properties in sulfated zirconia. Acidic properties are essential factors in affecting catalytic properties of alkylation.…”