Masazumi Tamura

Cs ₂ O-modified CeO ₂ exhibited high catalytic performance for the synthesis of β-alkoxyacrylates from alkynes and dialkyl carbonates as the first heterogeneous catalyst, affording the desired acrylates in high yields (up to 99%).

Direct amination of alcohols is an attractive synthetic method of secondary amines as water is generated as the sole byproduct. Solid acid catalysts have been developed with the advantages of their high stability and easily tunable acid nature. Herein, we report the synergistic effects of the Brønsted and Lewis acid sites of Nb2O5 on the amination of alcohols. Calcination of Nb2O5 altered the ratio of Brønsted acid sites to Lewis acid sites along with the removal of water, promoting the direct amination of alcohols. Nb2O5 calcined at 573 K (Nb2O5-573) acted as a reusable heterogeneous catalyst for the direct amination of alcohols to give the corresponding secondary amines in high yields. The formation rate per acid site of Nb2O5-573 was 21.7 h–1, which is higher than those of the previously reported solid acid catalysts (0.4–8.5 h–1). A variety of alcohols and aromatic amines were applicable with this catalytic system to afford the corresponding secondary amines in moderate to high yields. Catalyst characterizations and control experiments using chiral alcohols demonstrated that the direct amination of alcohols over Nb2O5 mainly proceeded through an SN2-type nucleophilic substitution mechanism, whereas an SN1-type nucleophilic substitution mechanism has been proposed for the previously reported solid acid catalysts. Both Brønsted and Lewis acid sites interact with the hydroxy group of alcohols to enhance the leaving ability of the hydroxy group, resulting in the improvement of nucleophilic substitution by amines.

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.

Silica‐supported Rh catalyst (Rh/SiO ₂ ) is an effective catalyst for the transformation of isosorbide to value‐added triols and diols; however, the underlying reaction pathways remain insufficiently understood. In this work, we examine the kinetics of isosorbide hydrogenolysis, along with hydrogenolysis of representative model compounds over an Rh/SiO ₂ catalyst to clarify the substrate structure–reactivity relationships. Based on the dependence of substrate concentration and hydrogen pressure, the hydrogenolysis of C─O or C─C bonds is the rate‐determining step of isosorbide hydrogenolysis over Rh/SiO ₂ . From comparisons of reactivity and selectivity using various model substrates, it is evident that the ring‐opening cleavage of the ether C─O─C bond is much more reactive than that of C─OH bond. Furthermore, an investigation combining product distribution tendency using 3‐hydroxy‐THF as a model substrate for isosorbide revealed that simultaneous cleavage of the C─O─C and the C─OH bonds also occurs. Two dominant pathways for the hydrogenolysis of isosorbide are as follows: (i) ring‐opening cleavage of the C─O─C bond alone and (ii) simultaneous cleavage of the C─O─C and the C─OH bonds, which can explain the formation of the main products (1,6‐hexanediol, 3,4‐hexanediol, and 1,2‐pentanediol) from isosorbide. These insights clarify the reaction behavior over Rh/SiO ₂ , providing guidance for the rational design of catalysts for the hydrogenolysis of isosorbide and related biomass‐derived substrates.

Catalytic strategies for the synthesis of C5–C6 polyols from biomass and biomass-derivatives while preserving the original carbon chain length.

The hydrogenation of nicotinamide analogs using a Pt/SiO ₂ catalyst, followed by hydride transfer to NAD ⁺ , accomplished the highly selective regeneration of 1,4-NADH.

By using a Pt/SiO ₂ catalyst, the hydrogenation of N -benzyl nicotinamide, a structural mimic of the coenzyme NAD ⁺ required for enzymatic reactions, to 1,4-dihydro- N -benzyl nicotinamide was accomplished.