Influence of sulfate content in structural and porous characteristics of sulfated tin oxide ceramics

Reference	Presenter	Authors (Institution)	Abstract
17-028	Sandra Helena Pulcinelli	Alves-Rosa, M.A.(Instituto de Química/UNESP); Manaia, E.B.(Instituto de Química/UNESP); Pavan, M.S.(Instituto de Química/UNESP); Santilli, C.V.(Instituto de Química/UNESP); Pulcinelli, S.H.(Instituto de Química/UNESP);	The addition of sulfate groups to oxides increases the surface acidity and the enhancement of thermal stability of the oxides, favoring application as catalysts. Furthermore, the interactions between these groups and SnO2 nanoparticles stabilize the crystallites in small dimensions, keeping the SnO2 surface free from aggregation and acting as driver for the porous structure. Wet impregnation is the route most known to insert sulfate groups on the tin oxides surface. The incorporation of sulfate during the oxide synthesis by the sol-gel process must decrease steps in the preparation and benefit homogeneity of sulfate distribution. Different Sn4+:SO42- molar ratios were evaluated in the SnO2 characteristics. Results showed the oxide-sulfate bonds formed by uni- and bidentate complexes in the tetragonal SnO2 ceramic powders independent of the sulfate amount. Crystallites size and radius of gyration obtained from XRPD and SAXS are higher in the sample free of sulfate (13.5 and 7.7nm, respectively), decreasing in function of the sulfate amount to sizes around 7nm and radius of 3nm. The porous structure generated by the gel network of the sulfated SnO2 consists in elongated pores with main diameter of 3.3nm and surface area up to 135m2/g. The sulfate groups introduction have allowed to obtain smaller particles size and mesopores with narrow pore size distribution than in the oxide free of sulfate. The catalytic reaction of isopropanol dehydration was accompanied in situ by XAS and mass spectroscopy for evaluating the local order around tin atoms. The sulfate groups disturb the oxide network, causing decreases in the Sn-Sn coordination shell. Higher reaction temperatures caused increase of the disorder and higher Debye–Waller factor values were observerd. The isopropanol conversion in propene increases in function of the sulfate amount and surface areas until reaches 1:1 Sn2+:SO42- ratio, indicating the rise of surface acidity and potential for act as acidy catalyst.
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