ZrW catalyzed cellulose conversion in hydrothermal conditions: Influence of the calcination temperature and insights on the nature of the active phase

• Published in: Molecular catalysis 2019-10, Vol.476 (-), p.110518, Article 110518
• Main Authors: Nguyen, Van Chuc, Dandach, Amar, Vu, Thi Thu Ha, Fongarland, Pascal, Essayem, Nadine
• Format: Article
• Language: English
• Subjects: Catalysis; Cellulose liquefaction; Chemical Sciences; Environment and Society; Environmental Sciences; Glycolic acid; Lactic acid; Tungstated zirconia; Zirconium oxyhydroxide
• ISSN: 2468-8231; 2468-8231
• DOI: 10.1016/j.mcat.2019.110518

We report here a comparison between calcined and un-calcined ZrW to that of zirconium oxyhydroxide and calcined zirconia in the hydrolysis of cellulose. The results stress that the active phase of the Zr based catalysts might combine the couple Zr4+ and OH− species while the role of W species would be of secondary importance and contribute to enhance the overall acid strength and the amount of acid sites. Of prime importance, it is disclosed that un-calcined ZrW exhibits a higher stability than calcined ZrW against W leaching. [Display omitted] •We report here a comparison between calcined/un-calcined ZrW and zirconium oxyhydroxide / zirconia in the hydrolysis of cellulose.•The active phase of the Zr based catalysts might combine the couple Zr4+ and OH− species while the W species would be of secondary importance.•The role of W species contributes to enhance the overall acid strength and the amount of acid sites as prove by calorimetry of NH3 adsorption.•Un-calcined ZrW presents a higher stability in hot water than the calcined catalyst against W leaching. Tungstated zirconia, ZrW, is reported as an efficient solid acid catalyst in the conversion of cellulose into lactic acid in hydrothermal conditions. The active phase of ZrW is generally ascribed to more or less polymerized WOx domains dispersed on zirconia. In this study, commercial uncalcined and calcined tungstated zirconia were used as catalysts for the conversion of cellulose under hydrothermal conditions at 190 °C. Their activities were also compared with uncalcined zirconium oxyhydroxide, ZrO2-x(OH)2x and calcined zirconia, ZrO2. Contrary to the expected results, it is disclosed that uncalcined ZrW exhibits higher catalytic activity and stability than calcined ZrW. Modifications in the products distribution were observed as glycolic acid formation at the expense of lactic acid formation upon ZrW calcination. Even more surprising, the catalytic activity of W free amorphous zirconium oxyhydroxide ZrO2-x(OH)2x is similar to uncalcined ZrW, with lactic acid as the main product while ZrO2 does not have any catalytic activity. These results suggest that the active phase of these catalysts might combine the couple Zr4+ and OH− species while the role of W species would be of secondary importance.