The surface structure of sulfated zirconia : Studies of XPS and thermal analysis

Isomerization of n-Butane over Sulfated Al- and Ga-Promoted Zirconium Oxide Catalysts. Influence of Promoter and Preparation Method

The designed model SO42-/Fe2O3-SiO2 catalysts with varied acidic strength and Bronsted acid sites were successfully prepared. The properties of acid sites can be regulated by preparation method and silica incorporation. The S/Fe sample without silica had stronger acid strength, more Bronsted acid sites and higher acid density, which showed the best catalytic performance. NH3-TPD, pyridine-IR and methanol/dimethoxymethane adsorption-desorption techniques were employed to reveal the relationship between acid properties of the catalysts and catalytic activity for the reaction of trioxane with methanol. Further, this reaction is determined by the strength of acid sites on catalyst surface and does not affect by the inner pore diffusion. These findings suggest that the catalytic activity and selectivity can be monitored mainly by acid strength and Bronsted acid sites on the sulfated oxides, while trioxane decomposition process seems to be a vital step and polyoxymethylene hemiacetals are supposed to be the key intermediates. Meanwhile, a large number of acid sites and a higher surface area of the catalysts can also improve the catalytic performance. These results should provide some specific guidance for understanding of the reaction mechanism and the catalyst design. (C) 2014 Elsevier B.V. All rights reserved.

Designed SO42−/Fe2O3-SiO2 solid acids for polyoxymethylene dimethyl ethers synthesis: The acid sites control and reaction pathways

This paper examines the effect of sulfation of vanadia-titania binary solid prepared by sol-gel process on its activity for the selective catalytic reduction (SCR) of NO with NH3. Sulfated and unsulfated vanadia titania have been characterized by means of N-2 adsorption-desorption at 77 K, XRD, TGA, propan-2-ol conversion as acid test, H-2-TPR measurements, EPR, XPS and Raman spectroscopies. The main results of this study highlight the interaction of sulfate ions with vanadia species. The ternary catalyst VTiS exhibits a high activity compared to binary TiS or VTi samples. It is concluded that sulfate species improve the superficial acidity of solid and interact with vanadia leading to a better reducibility of VTiS oxide. (c) 2006 Elsevier B.V. All rights reserved.

Selective catalytic reduction of NO by ammonia on V2O5-SO42-/TiO2 catalysts prepared by the sol-gel method

Mesoporous nanocrystalline sulfated zirconia catalyst has been prepared from zirconium hydroxide synthesized at different digestion/hydrothermal treatment times. Sulfuric acid and chlorosulfonic acid were used as two different sulfonating agents. The effect of digestion time, sulfonating agent and the calcination temperature on structural, textural and catalytic properties of the prepared catalyst were investigated in details using nitrogen adsorption–desorption (BET), ammonia temperature programmed desorption (NH3-TPD), X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TGA–DSC), and Fourier transform infrared spectroscopy (FTIR). The sulfated zirconia prepared at various digestion times and two different sulfonating agents were tested for the esterification of free fatty acid (FFAs) in soybean oil (prepared by mixing oleic acid in soybean oil) as model reaction. Sulfated zirconia catalyst prepared with 3 h digestion time and 600 °C calcination temperature using chlorosulfonic acid showed the highest catalytic activity with about 85% conversion in just 80 min of esterification time at 60 °C reaction temperature.

Mesoporous nanocrystalline sulfated zirconia synthesis and its application for FFA esterification in oils

Two series of sulfated zirconia have been prepared by immersing amorphous or crystalline zirconia in an H2SO4 solution (0.25–2.5 M). They were compared with a commercial sulfated zirconium hydroxide. Activation temperature was varied between 300 and 725°C. Sulfate density varied so that the mean surface area of an individual sulfate ranged from 0.14 to 0.54 nm2. Three limiting sulfate states are evidenced and characterized by TPR‐MS. Catalysts are tested for isomerization of n‐hexane at 150°C and 3 MPa. Factors influencing the activity are discussed. The data show that a highly active and selective catalyst for producing hexane isomers requires tetragonal zirconia with a sulfate occupancy of about 0.40 nm2. Preparation parameters must therefore be adapted to match these constraints.

A.K. Søiland

Papers

Influence of sulfation and structure of zirconia on catalytic isomerization of n‐hexane