Isotopic transient analysis of the ethanol coupling reaction over magnesia

Birky, Theodore W.; Kozlowski, Joseph T.; Davis, Robert J.

doi:10.1016/j.jcat.2012.11.014

Cited by 98 publications

(143 citation statements)

References 52 publications

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“…Studies of Guerbet condensation with catalysts having acid-base bifunctionality show that dehydration rates are higher on more acidic materials, whereas dehydrogenation is favorable over basic sites. The effect is clearly visible when materials with tunable acid-base functionality are used, such as Mg/Al mixed oxides, 72,95,115 hydroxyapatites, 121 Mg/Zr mixed oxides 103 and Na-doped ZrO 2 . 69 Materials containing more and stronger acid sites facilitate undesirable dehydration reactions.…”

Section: By-product Formationmentioning

confidence: 99%

See 1 more Smart Citation

Review of catalytic systems and thermodynamics for the Guerbet condensation reaction and challenges for biomass valorization

Gabriëls

Hernández

Sels

et al. 2015

Catal. Sci. Technol.

249

233

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The Guerbet condensation reaction is an alcohol coupling reaction that has been known for more than a century. Because of the increasing availability of bio-based alcohol feedstock, this reaction is of growing importance and interest in terms of value chains of renewable chemical and biofuel production. Due to the specific branching pattern of the alcohol products, the Guerbet reaction has many interesting applications. In comparison to their linear isomers, branched-chain Guerbet alcohols have extremely low melting points and excellent fluidity. This review provides thermodynamic insights and unravels the various mechanistic steps involved. A comprehensive overview of the homogeneous, heterogeneous and combined homogeneous and heterogeneous catalytic systems described in published reports and patents is also given. Technological considerations, challenges and perspectives for the Guerbet chemistry are discussed.

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Section: By-product Formationmentioning

confidence: 99%

“…In one report, the authors prepared Mg/Zr mixed oxides by various methods for the Guerbet condensation of ethanol. 103 Addition of Zr to the MgO catalyst however increased the acid site density and hence dehydration reactions of ethanol to ethane. The addition of Zr therefore appeared detrimental to the catalytic performance of MgO.…”

mentioning

confidence: 99%

Review of catalytic systems and thermodynamics for the Guerbet condensation reaction and challenges for biomass valorization

Gabriëls

Hernández

Sels

et al. 2015

Catal. Sci. Technol.

249

233

View full text Add to dashboard Cite

show abstract

“…In particular, MgO appears to be the standard material used in these reactions [87][88][89]. According to the results obtained, temperatures higher than 300 °C are needed to observe ethanol conversion, but only acetaldehyde can be observed at temperatures under 400 °C.…”

Section: Ethanol Condensation Catalysts and Reaction Mechanismmentioning

confidence: 96%

Base-Catalyzed Reactions in Biomass Conversion: Reaction Mechanisms and Catalyst Deactivation

Faba

Dı́az

Ordóñez

2016

Green Chemistry and Sustainable Technology

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Although less studied than acid-catalyzed reactions, mainly because of their marginal interest in petrochemical processes, base-catalyzed reactions (either homogeneous or heterogeneous) play a key role in the upgrading of biomass-derived platform molecules. As in most of the chemical processes, the replacement of homogeneous catalysts by heterogeneous catalysts is of key interest. This article reviews the state of the art in the most important base-catalyzed reactions in the biofuel manufacture (biodiesel from triglycerides) and the upgrading of biomass-derived platform molecules (such as acetone, ethanol, furfural, 5-hydroxymethylfurfural, or acetic acid). Transesterification reactions, aldol condensation (alone or in combination with other reactions), and ketonization are the main reactions involved in these biorefinery processes. Reviewed are the most common catalysts proposed for these reactions (mainly heterogeneous), as well as the proposed mechanisms for these reactions, and the main factors governing catalyst deactivation when used in each of these reactions.

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“…Therefore, the influence of Na addition to ZrO 2 on the ethanol coupling rate is likely related to how Na affects other aspects of the ethanol coupling reaction. Recent work in our lab utilizing isotopic transient methods and IR spectroscopy to study the coupling of ethanol over MgO at 673 K revealed a very high coverage of dissociated ethanol on the surface during reaction and very little coverage of reactive intermediates leading to coupling products [189]. The high coverage of ethoxide and surface hydroxide that was also likely to be present on ZrO 2 and Na-loaded ZrO 2 surfaces during ethanol coupling reactions likely inhibited C-C coupling reactions as was seen in the case with MgO [189].…”

Section: Resultsmentioning

confidence: 99%

“…Recent work in our lab utilizing isotopic transient methods and IR spectroscopy to study the coupling of ethanol over MgO at 673 K revealed a very high coverage of dissociated ethanol on the surface during reaction and very little coverage of reactive intermediates leading to coupling products [189]. The high coverage of ethoxide and surface hydroxide that was also likely to be present on ZrO 2 and Na-loaded ZrO 2 surfaces during ethanol coupling reactions likely inhibited C-C coupling reactions as was seen in the case with MgO [189]. We suspect that Na promotes aldol condensation on ZrO 2 catalysts (as observed in Table 5.5), but during the complex sequence of steps comprising the ethanol coupling reaction, the aldol condensation steps are more affected by the inventory of adsorbed ethoxide and hydroxide formed in situ rather than the Na present on the surface.…”

Section: Resultsmentioning

confidence: 99%

Carbon-Carbon Bond Forming Reactions Over Metal Oxide Catalysts

Kozlowski¹

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Alcohol coupling, also known as the Guerbet reaction, is a potentially important process to increase the value of short chain alcohols. Metal oxides, metal phosphates and supported transition metals like copper are some examples of heterogeneous catalysts for the reaction.However, the wide variety of catalyst compositions, reaction conditions, and reactor configurations used to study the reaction complicates a direct comparison of various catalysts.Herein, rates over different catalysts will be compared. One existing gap in the current literature is a thorough comparison of the surface acid and base properties of catalysts employed in the Guerbet coupling of alcohols. In this work, various bifunctional materials were synthesized, characterized, and used in Guerbet alcohol coupling and other probe reactions of acid and base catalysts.One well-studied reaction catalyzed by acids and bases is transesterification. Two series of Mg:Zr mixed oxides, prepared by either co-precipitation or sol-gel synthesis, were characterized and evaluated in the base-catalyzed transesterification of tributyrin with methanol.A co-precipitated Mg-rich mixed oxide catalyst with Mg:Zr 11:1 was approximately 300% more active than MgO on a surface area basis, whereas pure ZrO 2 was inactive for the reaction. To explore the nature of the activity enhancement, samples were characterized by X-ray diffraction, N 2 adsorption, CO 2 adsorption microcalorimetry and DRIFTS of adsorbed CO 2 and CH 3 OH.Although the sol-gel synthesis method provided better atomic-level mixing of Mg and Zr, the resulting catalysts were not as effective as mixed oxides prepared by co-precipitation. The most active mixed oxide (Mg:Zr 11:1) exhibited a high initial heat of CO 2 adsorption and modified modes of methanol adsorption compared to MgO. However, the CO 2 adsorption capacity did not correlate to catalyst activity.

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Isotopic transient analysis of the ethanol coupling reaction over magnesia

Cited by 98 publications

References 52 publications

Review of catalytic systems and thermodynamics for the Guerbet condensation reaction and challenges for biomass valorization

Review of catalytic systems and thermodynamics for the Guerbet condensation reaction and challenges for biomass valorization

Base-Catalyzed Reactions in Biomass Conversion: Reaction Mechanisms and Catalyst Deactivation

Carbon-Carbon Bond Forming Reactions Over Metal Oxide Catalysts

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