Synthesis of 2‐Butanol by Selective Hydrogenolysis of 1,4‐Anhydroerythritol over Molybdenum Oxide‐Modified Rhodium‐Supported Silica

Abstract

Rh-MoOx /SiO2 (Mo/Rh=0.13) is an effective catalyst for the hydrogenolysis of 1,4-anhydroerythritol (1,4-AHERY) and provides 2-BuOH in high yield of 51 %. This is the first report of the production of 2-BuOH from 1,4-AHERY by hydrogenolysis. 1,4-AHERY was more suitable as a starting material than erythritol because the 2-BuOH yield from erythritol was low (34 %). Based on the kinetics and comparison of reactivities of the related compounds using Rh-MoOx /SiO2 and Rh/SiO2 catalysts, the modification of Rh/SiO2 with MoOx leads to the high activity and high selectivity to 2-BuOH because of the generation of reactive hydride species and the strong adsorption of 1,4-AHERY on MoOx species. The reaction proceeds by main two routes, (I) the combination of single C-O hydrogenolysis with the desorption of intermediates, a usual route in hydrogenolysis, and (II) multiple C-O hydrogenolysis without the desorption of intermediates from the active site, and the reaction mechanism for Route (II) is proposed.

Selective C−O Hydrogenolysis of Erythritol over Supported Rh‐ReOx Catalysts in the Aqueous Phase

“…However, as the pressure increased from 30 to 120 bar, the initial rate over Rh‐ReO x /TiO 2 increased slowly to 461 mmol ERY g Rh −1 h −1 , whereas it increased nearly linearly over Rh‐ReO x /ZrO 2 up to 1583 mmol ERY g Rh −1 h −1 . These results show a nearly first‐order kinetics in H 2 pressure over the ZrO 2 ‐supported catalyst in the range of pressure considered, which indicates that the H 2 is involved in the rate‐determining step and suggests that one active hydrogen species is produced from one H 2 molecule . In contrast, the order was positive but close to zero over the TiO 2 ‐supported catalyst.…”

“…In contrast, the order was positive but close to zero over the TiO 2 ‐supported catalyst. This suggests that the attack of the hydrogen active species is not the rate‐determining step, and the C−O bond cleavage in the substrate can be the rate‐determining reaction . These observations of the initial rates over two catalysts explain the large difference in the time to reach approximately 80 % conversion between the two catalysts at 80 bar H 2 (8 vs. 25 h; Table ).…”

“…The diols may be formed from ERY by different routes: (i) ERY may first undergo hydrogenolysis to the two butanetriols and, subsequently, to the diols; hydrogenolysis of 1,2,3‐BTO will produce 2,3‐BDO, 1,2‐BDO, and 1,3‐BDO, whereas the hydrogenolysis of 1,2,4‐BTO will produce 1,2‐BDO, 1,3‐BDO, and 1,4‐BDO (Scheme ), (ii) they may also be formed by the ring‐opening hydrogenolysis of 1,4‐AE via 3OH‐THF; however, only 1,2‐ and 2,3‐BDO will be produced by this route, (iii) elimination of two hydroxyl groups directly from ERY; BDOs are formed from the start of the reaction (Figure ), which suggests the feasibility of this last route; moreover, this mechanism agrees well with the proposition of Tomishige et al. on the possibility of the direct hydrogenolysis of 1,4‐AE to 2‐BuOH without the desorption of the intermediates from the active site over a Rh‐MoO x catalyst . As an attempt to identify the preferential mechanism (i, ii, iii), we looked at the selectivity to the different butanediols and butanols during the hydrogenolysis of the butanetriols and 1,4‐anhydroerythritol.…”

“…ERY is converted to the desired butanetriols (1,2,3‐BTO and 1,2,4‐BTO) and butanediols (BDO) by C−O bond cleavage. The overhydrogenolysis of BDO yields 1‐butanol (1‐BuOH) and 2‐butanol (2‐BuOH) . In addition, the dehydration of ERY can occur to yield 1,4‐anhydroerythritol (1,4‐AE); the successive C−O hydrogenolysis generates the formation of 3‐hydroxytetratydrofuran (3OH‐THF) and tetrahydrofuran (THF).…”

Valorization of Biomass‐derived Small Oxygenates: Kinetics, Mechanisms and Site Requirements of H2‐involved Hydrogenation and Deoxygenation Pathways over Heterogeneous Catalysts

“…With low temperatures (∼400 K) and high H 2 pressures (5–8 MPa) over these catalysts, decarbonylation is undetectable in the liquid‐phase, meaning the preservation of carbon value and dismissing any effect of CO* on C−O hydrogenolysis. The solvent of choice ranged from pure water, or pure alkanes to mixtures of alkanes and water, with this choice not affecting the active site structure as concluded based on EXAFS analyses . Some primary alcohols (C 4 and C 5 ) reacted at faster rates than secondary alcohols on Ir−ReO x or Rh−MoO x domains,, while some (propanols and hexanols) showed the opposite trend (note: C−O bonds are a few kJ mol −1 stronger in secondary short‐chain alcohols than in primary alcohols) .…”