Selective C−O Bond Cleavage of Bio‐Based Organic Acids over Palladium Promoted MoO_x/TiO₂

Abstract

Hydrodeoxygenation chemistries play a key role in the upgrading of biomass‐derived feedstocks. Among these, the removal of targeted hydroxyl groups through selective C−O bond cleavage from molecules containing multiple functionalities over heterogeneous catalysts has shown to be a challenge. Herein, we report a highly selective and stable heterogeneous catalyst for hydrodeoxygenation of tartaric acid to succinic acid. The catalyst consists of reduced Mo5+ centers promoted by palladium, which facilitate selective C−O bond cleavage, while leaving intact carboxylic acid end groups. Stable catalytic performance over multiple cycles is demonstrated. This catalytic system opens up opportunities for selective processing of biomass‐derived sugar acids with a high degree of chemical functionality.

Supported Bifunctional Molybdenum Oxide-Palladium Catalysts for Selective Hydrodeoxygenation of Biomass-Derived Polyols and 1,4-Anhydroerythritol

“…Interestingly, 3-hydroxytetrahydrofuran was not observed as a reaction intermediate even at very low conversions (<10%), suggesting that OH removal was not sequential. However, this behavior is substrate-structure-dependent, since in our prior studies we showed that tartaric acid conversion over similar catalytic systems proceeded through sequential C–O bond cleavage …”

“…Monometallic catalysts MoO x /TiO 2 (2 wt % Mo) and Pd/TiO 2 (0.3 wt % Pd) were prepared by incipient wetness impregnation of aqueous solutions of (NH 4 ) 6 Mo 7 O 24 ·4H 2 O and Pd­(NO 3 ) 2 ·2H 2 O on TiO 2 (P25) as reported previously by Nacy et al Monometallic catalysts were then dried overnight at 393 K and calcined in air at 773 K for 3 h. The MoO x -M/TiO 2 (2 wt % Mo, M/Mo molar ratio = 0.14) catalysts with varying hydrogen dissociating metal (M = Pd, Pt, Rh) were prepared by incipient wetness impregnation of aqueous solutions of Pd­(NO 3 ) 2 ·2H 2 O, H 2 PtCl 6 ·6H 2 O, and RhCl 3 · x H 2 O on TiO 2 (P25); followed by drying at 393 K for 12 h. The samples were then impregnated with an aqueous solution of (NH 4 ) 6 Mo 7 O 24 ·4H 2 O, dried at 393 K for 12 h, and calcined in air at 773 K for 3 h. For supported catalyst M′O x -Pd/TiO 2 (2 wt % M′, Pd/M′ molar ratio = 0.14) with varying oxophilic metals (M′ = Mo, Re, W), an aqueous solution of Pd­(NO 3 ) 2 ·2H 2 O was deposited by incipient wetness on TiO 2 (P25), then dried at 393 K for 12 h. The dried powders were then impregnated with (NH 4 ) 6 Mo 7 O 24 ·4H 2 O, NH 4 ReO 4 , and (NH 4 ) 10 W 12 O 41 · x H 2 O; dried at 393 K for 12 h; and calcined in air at 773 K for 3 h. Catalysts with varying supports were prepared by incipient wetness impregnation of aqueous solutions of Pd­(NO 3 ) 2 ·2H 2 O on TiO 2 (P25), ZrO 2 , γ-Al 2 O 3 , and SiO 2 . After drying the samples at 393 K for 12 h, an aqueous solution of (NH 4 ) 6 Mo 7 O 24 ·4H 2 O was deposited by incipient wetness impregnation prior to calcination in air at 773 K for 3 h. Metal loadings on the catalyst with varying supports was 0.3 wt % Pd and 2 wt % Mo.…”

“…An alternative redox-active metal with similar properties to Re is molybdenum (Mo). , We have recently shown via density functional theory (DFT) calculations that supported monomeric MoO x on TiO 2 is effective at C–O bond cleavage of 1,4-AHERY by DODH to produce 2,5-DHF . We have also shown that MoO x coupled with Pd on TiO 2 can catalyze the HDO of biomass-derived substrates containing carboxylic acid moieties, such as tartaric acid to produce succinic acid . These studies showcase the flexibility of supported MoO x species in a reducing environment to selectively cleave C–O bonds in substrates with multiple functional groups.…”

“…28 We have also shown that MoO x coupled with Pd on TiO 2 can catalyze the HDO of biomass-derived substrates containing carboxylic acid moieties, such as tartaric acid to produce succinic acid. 33 These studies showcase the flexibility of supported MoO x species in a reducing environment to selectively cleave C−O bonds in substrates with multiple functional groups.…”

Titania-supported molybdenum oxide combined with Au nanoparticles as a hydrogen-driven deoxydehydration catalyst of diol compounds

“…Pagán-Torres et al have very recently reported that MoO x –Pd/TiO 2 catalyzes the reduction of tartaric acid to succinic acid which is the product of DODH + hydrogenation with H 2 as a reducing agent; however, the proposed main reaction pathway is successive C–O bond cleavage via malic acid rather than DODH + hydrogenation. 55 Heyden et al have recently suggested that monomeric Mo species on TiO 2 can work as a DODH catalyst with a DFT-calculated free energy barrier of 1.5 eV at the C–O bond dissociation step. 56 In this study, we investigated the catalysis of MoO x –Au/TiO 2 for the reduction of polyols with H 2 as a reducing agent.…”