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

作者：Lloyd Rhys; Hansen Thomas W; Ranke Wolfgang; Jentoft Friederike C^*; Schloegl Robert

来源：Applied Catalysis A: General , 2011, 391(1-2): 215-224.

DOI：10.1016/j.apcata.2010.06.028

• Sulfated zirconia
• Model system
• TEM
• XPS
• UPS
• Butane
• Heats of adsorption

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 similar to 3 at.%) of active powder catalysts. The n-butane adsorption-desorption equilibrium under isobaric conditions (10(-8)-10(-6) h Pa) 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 similar to 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 similar to 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.

• 出版日期2011-1-4