Acid and redox properties of tungstated zirconia catalysts

Kourieh, Reem; Bennici, Simona; Auroux, A.

doi:10.1007/s11144-011-0385-1

Cited by 8 publications

(6 citation statements)

References 31 publications

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“…[67] They are active and stable during cellobiose hydrolysis if the tungsten condensation is high enough to form strong Brønsted acid sites, validating the role of Brønsted and Lewis acidities in the hydrolysis reaction (Table 3, entry 17). [67] They are active and stable during cellobiose hydrolysis if the tungsten condensation is high enough to form strong Brønsted acid sites, validating the role of Brønsted and Lewis acidities in the hydrolysis reaction (Table 3, entry 17).…”

Section: Other Oxidesmentioning

confidence: 69%

“…Indeed, tungstated zirconias are known as efficient acid catalysts, bearing Lewis and/or Brønsted acid sites depending on the tungsten content and dispersion. [67] They are active and stable during cellobiose hydrolysis if the tungsten condensation is high enough to form strong Brønsted acid sites, validating the role of Brønsted and Lewis acidities in the hydrolysis reaction ( Table 3, entry 17). [65] Layered mixed transition metal oxides (HNbMoO 6 , HTiNbO 5 and HTaMoO 6 ) have been presented by Takagaki et al.…”

Section: Other Oxidesmentioning

confidence: 69%

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Hydrolysis of Oligosaccharides Over Solid Acid Catalysts: A Review

et al. 2014

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Mild fractionation/pretreatment processes are becoming the most preferred choices for biomass processing within the biorefinery framework. To further explore their advantages, new developments are needed, especially to increase the extent of the hydrolysis of poly‐ and oligosaccharides. A possible way forward is the use of solid acid catalysts that may overcome many current drawbacks of other common methods. In this Review, the advantages and limitations of the use of heterogeneous catalysis for the main groups of solid acid catalysts (zeolites, resins, carbon materials, clays, silicas, and other oxides) and their relation to the hydrolysis of model soluble disaccharides and soluble poly‐ and oligosaccharides are presented and discussed. Special attention is given to the hydrolysis of hemicelluloses and hemicellulose‐derived saccharides into monosaccharides, the impact on process performance of potential catalyst poisons originating from biomass and biomass hydrolysates (e.g., proteins, mineral ions, etc.). The data clearly point out the need for studying hemicelluloses in natura rather than in model compound solutions that do not retain the relevant factors influencing process performance. Furthermore, the desirable traits that solid acid catalysts must possess for the efficient hemicellulose hydrolysis are also presented and discussed with regard to the design of new catalysts.

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Section: Other Oxidesmentioning

confidence: 69%

Section: Other Oxidesmentioning

confidence: 69%

Hydrolysis of Oligosaccharides Over Solid Acid Catalysts: A Review

et al. 2014

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“…A representative DRIFTS spectrum for the adsorption of pyridine onto the Zn x Zr y O z catalyst with 2.2 wt % Zn at 393 K is shown in Figure e. Bands at 1609, 1575, and 1444 cm –1 are characteristic of pyridine adsorbed on Lewis acid sites; however, the absence of bands at 1639 and 1540 cm –1 , corresponding to the pyridinium ion, suggests that there are no Brønsted acid sites present. , DRIFTS-py spectra for ZnO, ZrO 2 , and Zn x Zr y O z samples with Zn weight loadings of 1.6–8.0% are shown in Figure S2. For each of these catalysts, including monoclinic ZrO 2 , Lewis acid sites were observed but none of the catalysts contained significant Brønsted acid sites.…”

Section: Resultsmentioning

confidence: 99%

Mechanism and Kinetics of Isobutene Formation from Ethanol and Acetone over Zn_xZr_yO_z

2019

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Isobutene is a specialty chemical used in the production of fuel additives, polymers, and other high-value products. While normally produced by steam cracking of petroleum naphtha, there is increasing interest in identifying routes to synthesizing isobutene from biomass-derived compounds, such as ethanol and acetone. Recent work has shown that zinc−zirconium mixed oxides are effective and selective catalysts for producing isobutene from ethanol. However, the reaction pathway, the roles of acidic and basic sites, and the role of water in promoting stability and selectivity are not yet clearly defined. In this study, a series of zinc− zirconium mixed oxides with tunable acid−base properties were synthesized and characterized with XRD, Raman spectroscopy, BET, CO 2 -TPD, NH 3 -TPD, and IR DRIFTS of adsorbed pyridine in order to probe the roles of acid and base sites for each step in the ethanol-to-isobutene reaction pathway. The observed reaction kinetics, supported by modeling of these kinetics, suggest that the reaction of ethanol to isobutene proceeds via a five-step sequence. Ethanol first undergoes dehydrogenation to acetaldehyde, which is then oxidized to acetic acid. This product undergoes ketonization to produce acetone, which dimerizes to form diacetone alcohol. The latter product either decomposes directly to isobutene and acetic acid or produces these products by dehydration to mesityl oxide and subsequent hydrolysis. The acetic acid formed undergoes ketonization to produce additional acetone. The dispersion of zinc oxide on zirconia was found to produce a balance between Lewis acidic and basic sites that prevent the loss of ethanol via dehydration to ethylene and promote the cascade reactions of ethanol and acetone to isobutene. Water, while inhibiting both isobutene and mesityl oxide formation, improves isobutene selectivity by suppressing side reactions such as unimolecular dehydration, acetone decomposition, and deactivation due to coke formation.

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“…As observed in Fig. 3a for the 12.6 wt% catalyst, bands at 1609 and 1444 cm À1 indicate the presence of Lewis-acid sites, and bands at 1639 and 1540 cm À1 indicate the presence of Brønsted acid sites upon addition of pyridine [30,43]. Extinction coefficients published by Emeis were used to determine the ratio of Brønsted-to Lewis-acid sites from the intensities of the bands at 1444 cm À1 and 1540 cm À1 [44].…”

Section: Catalyst Characterizationmentioning

confidence: 99%