Mizuho Yabushita

Rare sugars, monosaccharides that occur only rarely in nature, exhibit physicochemical and biological properties distinct from those of naturally abundant sugars such as D-glucose. Their widespread utilization has been hindered by limitations in existing production methods, which rely primarily on equilibrium-constrained biocatalytic cascades or on synthetic approaches requiring multiple steps or organic reagents. Here we show the one-pot heterogeneous catalytic epimerization of methyl glucosides into rare sugar derivatives over supported Ru catalysts under hydrogen atmosphere in water. Among the supported metals examined, Ru uniquely promotes regioselective stereoinversion of 1- O -methyl β-D-glucopyranoside at the C3 position to produce 1- O -methyl β-D-allopyranoside without requiring additional reagents or multistep reactions. Isotopelabeling experiments reveal that dehydrogenation and hydrogenation proceed substantially faster than net epimerization, identifying surface-confined molecular rotation of a keto intermediate as the rate-determining step. Computer simulations further show that the experimentally observed regioselectivity originates from the low rotational free energy barriers and relatively high stability of the keto intermediate on the Ru surface. These findings identify molecular rotational dynamics on catalyst surfaces as a governing principle for stereochemical inversion reactions.

Hydrogenation of amides with selective C–N bond cleavage over C–O scission remains challenging, especially under heterogenized molecular catalysis. Herein, we report the immobilization of a robust ruthenium complex on the surface of Merrifield resin (RuPCY2@MR) as a highly effective and selective heterogenized organometallic catalyst for the C–N bond cleavage of amides. Characterization of this complex was performed employing different techniques, including ICP-AES, IR, XRF, TGA, XPS, 31P CP/MAS NMR, and SEM. This heterogenized catalyst enables the hydrogenation of different unactivated aromatic and aliphatic amides with excellent selectivity toward C–N scission in up to 99% yield with low catalyst loadings (1 mol %). The heterogeneity of this catalyst was proven by a hot filtration test, and catalyst recycling was performed in up to three cycles.

Molybdenum-based catalysts were investigated for the hydrodeoxygenation of guaiacol to phenol under mild conditions. To compensate for the low hydrogen activation ability of Mo, various metals were tested as additives to modify the MoOx/TiO2 catalyst. Ag was found to be an effective additive metal, and hydrodeoxygenation of guaiacol proceeded over the MoOx-Ag/TiO2 catalyst at a lower temperature than previously reported, giving phenol in 59 mol % yield (503 K, H2 3 MPa). Methanol was the main C1 product derived from the methoxy group of guaiacol. The catalyst can be reused after calcination to remove surface-deposited organic species. The catalytic activity was sharply increased by the increase of Mo or Ag amount at low loading amount range and was slowly increased at a high amount range. The physically mixed catalyst of MoOx/TiO2 and Ag/TiO2 was much less active than MoOx-Ag/TiO2. These trends suggest that the catalytically active sites are bimetallic MoOx-Ag interface sites. TEM-EDX, XRD, H2-TPR, H2-TPD, XAS, reaction kinetics, and stoichiometric reaction with reduced catalyst suggest that highly dispersed Mo4+ species and nanosized Ag clusters on TiO2 are responsible for guaiacol hydrodeoxygenation, and the methoxy group is eliminated due to the oxophilic nature of Mo4+, leading to the formation of phenol.

One‐pot synthesis of asymmetric alkyl methyl carbonates from CO ₂ , methanol (MeOH), and various alcohols was demonstrated using CeO ₂ and 2‐cyanopyridine as a heterogeneous catalyst and dehydrating agent, respectively. The molar ratio of MeOH to the other alcohol and structure of the latter alcohol governed the distribution of three organic carbonates, that is, asymmetric alkyl methyl carbonate, dimethyl carbonate (DMC), and dialkyl carbonate. For primary alcohols such as ethanol, 1‐propanol, and 1‐butanol, an equimolar ratio of MeOH to the other alcohol afforded the highest distribution of the asymmetric alkyl methyl carbonate. In contrast, the low reactivity of 2‐propanol due to steric hindrance from its bulky alkyl moiety enabled the preferential formation of isopropyl methyl carbonate (iPMC) with >80% distribution among the three carbonates of iPMC, DMC, and diisopropyl carbonate. The time‐course study indicated the involvement of two reaction routes for synthesizing asymmetric organic carbonates: (i) direct cross‐carboxylation of MeOH, the other alcohol, and CO ₂ and (ii) transesterification between DMC, which is formed via homo‐carboxylation of MeOH and CO ₂ , and the other alcohol. In the case of iPMC synthesis, the indirect route (ii) became dominant because of the low reactivity of 2‐propanol.

The oxidation of 3,4‐dihydro‐2 H ‐pyran (DHP), which can be produced from lignocellulose‐derived furfural, was investigated with various catalysts and molecular oxygen as an oxidant in a H ₂ O solvent. 5,6‐Dihydro‐2 H ‐pyran‐2‐one (DHPO) was obtained in moderate yield with a carbon black‐supported Pd catalyst (Pd/C). The addition of base (NaHCO ₃ ) suppressed the side reaction of DHP (i.e., hydration of DHP) and increased DHPO yield up to 52%. The activity of the catalyst was slightly decreased after three‐time use but recovered by the heat‐treatment under H ₂ . Through the investigation of various Pd/support catalysts, the catalysts with low valent and stable Pd ⁰ phase during the reaction, such as Pd/C and Pd/BN, showed high activity in DHPO formation. Positive and almost zero reaction orders were observed with respect to O ₂ pressure and DHP concentration, respectively, indicating the involvement of oxygen species in the rate‐determining step and the strong adsorption of DHP with catalyst. The addition of radical scavenger lowered the formation amount of DHPO, suggesting that a radical intermediate is involved in the reaction.

Advantages/disadvantages of heterogeneous CeO ₂ and homogeneous DBU catalysts were fairly compared for the direct production of cyclic compounds from CO ₂ and either monoethanolamine or ethylenediamine via a detailed kinetic study.

Continuous conversion of CO ₂ -absorbed alkanolamines in the corresponding amine solvent was demonstrated with a fixed-bed flow reactor and a CeO ₂ catalyst. Both the reaction rate and pathway were governed by the alkyl chain length of alkanolamines.

Zeolites have been considered as key materials in the fields such as catalysis and adsorption due to their ease of tunability via isomorphous substitution with heteroatoms and surface decoration with metal/metal-oxide nanoparticles. The resulting function and performance of zeolites are well-known to be significantly dependent on their preparation methods. This review paper gathers some unique zeolites that were prepared hydrothermally from amorphous Si-based mixed metal oxides. The initial two examples, Ga-introduced MFI-type zeolites and MFI-type zeolites dually substituted by Al and Fe, exhibited the high selectivity to CO in the oxidative conversion of methane and the long lifetime in the reaction of dimethyl ether to olefins, respectively, as catalysts. The combination of Ce-decorated MFI-type zeolites and Pd nanoparticles enabled the oxidative conversion of methane at quite low reaction temperatures to produce ethane. The last examples overviewed in this paper were based on the intentional construction of paired heteroatom (Al or Ga) sites in CHA- and MFI-type zeolites, which behaved as ion-exchange sites for capturing divalent cations.