Gas-phase dehydration of glycerol over calcined tungsten-modified Zn–Al–O hydrotalcite-type catalysts

• ZnAl samples represent the layered ZnAl–CO3–LDH with a hydrotalcite-like structure.
• The modification of ZnAl samples with tungsten component changes SBET (90–110 m2/g).
• The introduction of tungsten component provides the increase in BAS concentration.
• The glycerol dehydration is determined by the state of the catalyst surface.
• The higher the Bronsted acid sites content, the larger the ratio of acrolein/acetol.

Zinc aluminum (ZA) samples with the ratio of Zn/Al > 2 prepared by deposition of a mixed solution of aluminum and zinc nitrates with an aqueous solution of precipitant and varied by the method of modification with tungsten-containing component were characterized by XRD, FTIR, and adsorption methods and tested in the reaction of glycerol dehydration. The properties of samples were studied depending on Zn/Al ratio (ZA-2, ZA-3), the nature of precipitant: NaOH (ZA-2) or NH4OH (ZA-2a), and the method of modification by introducing the [W12O41]10− anion into the interlayer space [ZA-2 (W), ZA-2a (W)] or by deposition of PW (SiW) heteropoly acid on the surface [PW (SiW)/ZA-2 (ZA-2a)]. It was shown that dried ZA-2 sample represented a layered Zn–Al hydroxide with a structure similar to hydrotalcite; ZA-2a and ZA-3 samples contained ZnO in addition to mentioned phase. The modification of ZnAl samples with W-containing component did not change the phase composition but reduced the degree of crystallinity. The thermal treatment of the samples in the interval of 450–600 °C promoted the formation of a solid solution based on ZnO which transformed after the calcination at 900 °C into mixture of ZnO and ZnAl2O4 phases. It was found that the surface of the studied samples contained both Bronsted (BAS) and Lewis acid sites (LAS). BAS concentration referred to m2 of the surface increased in the row: ZA-2a < ZA-2a(W) < SiW/ZA-2a, while the concentration of LAS decreased in the same row. The correlation between the amount of acrolein formed and BAS content on the sample surface, on the one hand, and between the ratio of acrolein/acetol and BAS/(sumLAS + BAS) ratio, on the other hand, was revealed.

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