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1. Deoxydehydration of 1,4-anhydroerythritol over anatase TiO ₂ (101)-supported ReO _x and MoO _x

   https://doi.org/10.1039/d0cy00434k  

   Xi, Yongjie; Lauterbach, Jochen; Pagan-Torres, Yomaira; Heyden, Andreas (June 2020, Catalysis Science & Technology)

   Heterogeneously catalyzed deoxydehydration (DODH) ordinarily occurs over relatively costly oxide supported ReO x sites and is an effective process for the removal of vicinal OH groups that are common in biomass-derived chemicals. Here, through first-principles calculations, we investigate the DODH of 1,4-anhydroerythritol over anatase TiO 2 (101)-supported ReO x and MoO x . The atomistic structures of ReO x and MoO x under typical reaction conditions were identified with constrained thermodynamics calculations as ReO 2 (2O)/6H–TiO 2 and MoO(2O)/3H–TiO 2 , respectively. The calculated energy profile and developed microkinetic reaction model suggest that both ReO 2 (2O)/6H–TiO 2 and MoO(2O)/3H–TiO 2 exhibit a relatively low DODH activity at 413 K. However, at higher temperatures such as 473 K, MoO(2O)/TiO 2 (101) was found to exhibit a reasonably high catalytic activity similar to ReO 2 (2O)/6H–TiO 2 , consistent with a recent experimental study. Mechanistically, the first O–H bond cleavage of 1,4-anhydroerythritol and the dihydrofuran extrusion were found to be the rate-controlling steps for the reaction over ReO 2 (2O)/6H–TiO 2 and MoO(2O)/3H–TiO 2 , respectively. Thus, this study clarifies the mechanism of the DODH over oxide-supported catalysts and provides meaningful insight into the design of low-cost DODH catalysts. 

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2. Highly efficient deoxydehydration and hydrodeoxygenation on MoS2-supported transition metal atoms through a C-H activation mechanism

   https://doi.org/10.1021/acscatal.0c02669  

   Xi, Yongjie; Heyden, Andreas (July 2020, ACS Catalysis)

   Deoxydehydration (DODH) is an efficient process for the removal of vicinal OH groups of a diol or polyol. Conventional DODH reactions usually take place at a single-site MOx (M=Re, Mo, V etc.) active center, which proceed through a diol condensation step, an alkene extrusion step and a catalyst regeneration (or reduction) step. Here, we suggest that MoS2-supported transition metal atoms allow for the DODH reaction to occur through an alternative mechanism, whereby the C-H bond of a diol is activated first, which facilitates the C-OH bond cleavage on a neighboring carbon. The removal of the second OH group is also facile over the proposed catalysts. Our kinetic studies suggest that the DODH of ethylene glycol on Ru2/MoS2, Ir2/MoS2 and Ru3/MoS2 are highly active with predicted turnover frequencies of over 1/s. Thus, our study suggests a possible approach for the design of highly active DODH catalysts. Apart from being a DODH catalyst, the proposed MoS2-supported catalysts are also highly active as hydrodeoxygenation catalyst for the removal of alcohol OH groups. 

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3. Transition metal-catalyzed deoxydehydration: missing pieces of the puzzle

   https://doi.org/10.1039/d1cy02083h  

   Jentoft, Friederike C. (October 2022, Catalysis Science & Technology)

   Deoxydehydration (DODH) is a transformation that converts a vicinal diol into an olefin with the help of a sacrificial reductant. The reaction has drawn interest in the past 25 years for its potential to upgrade polyols from biomass to chemicals or fuels. This minireview is organized in 7 sections, and, while providing a comprehensive survey of the literature in tabular form, focuses on aspects that are not extensively discussed in prior reviews. The first three brief sections consist of an introduction to DODH, followed by an overview of present research thrusts and a listing of prior reviews and the patent literature. The fourth section addresses reaction thermodynamics. The fifth section provides a survey of catalysts investigated for DODH, most of which are rhenium, molybdenum, and vanadium compounds. These catalysts have been used in heterogeneous and homogenous catalysis alike. The catalyst compositions are discussed including the effect of counterions that are not part of the active metal moiety. The sixth section reviews rate laws that have been formulated and the steps identified as rate controlling, by experiment or theory. Catalyst reduction and olefin extrusion emerge as key steps. In this context, the somewhat mysterious trends among alcohol reductants are inspected. It emerges that the DODH field would benefit from benchmark reactions that will quantitatively connect the collected catalytic data. The seventh section considers phase chemistry, separations, and energy input. 

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4. Deoxydehydration of polyols catalyzed by a molybdenum dioxo-complex supported by a dianionic ONO pincer ligand

   https://doi.org/10.1039/C9DT03759D  

   Tran, Randy; Kilyanek, Stefan M. (November 2019, Dalton Transactions)

   Deoxydehydration (DODH) is the net reduction of diols and polyols to alkenes or dienes and water. Molybdenum cis -dioxo bis-phenolate ONO complexes were synthesized and have been shown to be active for DODH. Catalysts were screened for activity at 150–190 °C, and appreciable yields of up to 59% were obtained. PPh 3 , Na 2 SO 3 , Zn, C, 3-octanol and 2-propanol were screened as reductants. Additionally, the reactivities of a variety of diols were screened. With ( R , R )-(+)-hydrobenzoin as substrate, DODH occurs via a mechanism where reduction of the Mo catalyst is a result of diol oxidation to form two equivalents of aldehyde. These reactions result in complete conversion and near quantitative yields of trans-stilbene and benzaldehyde. 

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5. Influence of the pendant arm in deoxydehydration catalyzed by dioxomolybdenum complexes supported by amine bisphenolate ligands

   https://doi.org/10.1039/D0NJ02151B  

   Siu, Timothy C.; Silva, Israel; Lunn, Maiko J.; John, Alex (January 2020, New Journal of Chemistry)

   Dioxomolybdenum complexes supported by aminebisphenolate ligands were evaluated for their potential in catalyzing the deoxydehydration (DODH) reaction to establish structure–activity relationships. The nature of the pendant arm in these aminebisphenolate ligands was found to be crucial in determining reactivity in the deoxydehydration of styrene glycol (1-phenyl-1,2-ethanediol) to styrene. Pendant arms bearing strongly coordinating N -based groups such as pyridyl or amino substituents were found to hinder activity while those bearing non-coordinating pendant arms (benzyl) or even weakly coordinating groups (an ether) resulted in up to 6 fold enhancement in catalytic activity. A dioxomolybdenum complex featuring an aminemonophenolate ligand derived from the aminebisphenolate skeleton also resulted in similar yield enhancements. Although aromatic solvents were found to be ideal for performing these catalytic reactions, polar solvents such as N , N -dimethylformamide (DMF) and N , N ′-dimethylpropyleneurea (DMPU) were also suitable. The catalyst was found to maintain its structural integrity under the optimized conditions and could be recycled for a second catalytic run without loss of activity. With the activated substrate meso -hydrobenzoin, trans -stilbene was obtained in a 56% yield at 220 °C along with benzaldehyde (71%) suggesting that the diol is a competing reductant under these conditions. 

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