Kenichi Kon

Hydrogenation of levulinic acid to γ-valerolactone by Ni and MoOx co-loaded carbon catalysts

To develop a noble metal-free heterogeneous catalyst for liquid phase hydrogenation of levulinic acid to γ-valerolactone under H2, we tested a series of base-metal (Ni, Co, Cu, and Fe) and metal oxides (Mo, V, and W oxides) co-loaded carbon (C) and Ni-loaded metal oxides for the reaction. Ni–MoOx/C pre-reduced at 500 °C showed the highest activity and showed more than 300 times higher turnover number (TON) than previously reported noble metal-free catalysts. A structure–activity relationship study showed that the co-presence of metallic Ni0 species and partially reduced MoO2 could be responsible for the high activity.

Sustainable heterogeneous platinum catalyst for direct methylation of secondary amines by carbon dioxide and hydrogen.

Pt and MoO(x) co-loaded TiO2 is found to be highly effective for direct methylation of aliphatic and aromatic secondary amines by CO2 and H2 under solvent-free conditions. This is the first additive-free and reusable heterogeneous catalytic system with acceptable turnover number.

Selective hydrogenation of levulinic acid to valeric acid and valeric biofuels by a Pt/HMFI catalyst

We describe one-pot high-yield catalytic pathways for the conversion of levulinic acid (LA) to valeric acid (VA) or valeric acid esters (so-called valeric biofuels) under relatively mild conditions (2 or 8 bar H2, 200 °C). A thorough screening study reveals that a HMFI zeolite-supported Pt metal cluster (Pt/HMFI) with an average cluster size of 1.9 nm shows the highest yield of VA (99%) under solvent-free conditions. The use of ethanol or methanol as solvent changes the selectivity, resulting in 81–84% yields of ethyl valerate (EV) or methyl valerate (MV). Pt/HMFI is also effective for selective formation of valeric acid esters from γVL in alcohols under H2. Kinetics, in situ infrared (IR), and acidity–activity relationship studies show a cooperative mechanism of Pt and Bronsted acid sites of HMFI. VA formation from LA can be driven by Pt-catalyzed hydrogenation of LA to γVL, which undergoes proton-assisted ring-opening by HMFI, followed by Pt-catalyzed hydrogenation. Valeric ester formation from LA is driven by esterification of LA to levulinic ester, which is hydrogenated by Pt.

Heterogeneous cobalt catalysts for the acceptorless dehydrogenation of alcohols

A series of transition metal(M)-loaded TiO2 catalysts (M/TiO2) and Co-loaded catalysts on various support materials were prepared by an impregnation method, followed by in situ H2-reduction at 400 °C, and tested for the acceptor-free oxidation of cyclododecanol in the liquid phase. Among the catalysts including noble metal catalysts, Co/TiO2 showed the highest activity. In the presence of Co/TiO2 (0.1–3 mol%) the dehydrogenation of various aliphatic secondary alcohols proceeded to afford the corresponding ketones. The catalyst was recoverable and was reused after the H2-reduction treatment. Based on the spectroscopic characterization of the catalyst combined with the studies on the effect of the Co oxidation states on the catalytic activity, it is clarified that the surface metallic Co sites with electron deficiency are the catalytically active species.

Hydrodeoxygenation of fatty acids and triglycerides by Pt-loaded Nb2O5 catalysts

Platinum nanoparticles loaded onto various supports have been studied for the selective hydrogenation of lauric acid to n-dodecane. The activity depends on the support material and pre-reduction temperature. Pt/Nb2O5 reduced at 300 °C gives the highest activity. Pt/Nb2O5 shows higher activity than various Nb2O5-supported transition metals (Ir, Re, Ru, Pd, Cu, Ni). Under solvent-free conditions Pt/Nb2O5 is effective for the hydrodeoxygenation of lauric, capric, palmitic, myristic, oleic, and stearic acids under 8 bar H2 at 180–250 °C, which gives high yields (88–100%) of linear alkanes with the same chain length as the starting compound. Tristearin is also converted to give 93% yield of n-octadecane. Pt/Nb2O5 shows more than 60 times higher turnover number (TON) than the previously reported catalysts for the hydrogenation of stearic acid to n-octadecane. Mechanistic study shows a consecutive reaction pathway in which lauric acid is hydrogenated to 1-dodecanol, which undergoes esterification with lauric acid as well as hydrogenation to n-dodecane. The ester undergoes hydrogenolysis to give the alcohol, which is hydrogenated to the alkane. Infrared (IR) study of acetic acid adsorption on Nb2O5 indicates that Lewis acid–base interaction of Nb cation and carbonyl oxygen, which suggests a possible role of Nb2O5 as an activation site of carbonyl groups during hydrodeoxygenation.

General and selective C-3 alkylation of indoles with primary alcohols by a reusable Pt nanocluster catalyst.

The platinum rule: Heterogeneous, additive-free C-3 selective alkylation of indoles by aliphatic and aromatic alcohols proceeded under transfer hydrogenation conditions with the reusable Pt/θ-Al2 O3 catalyst (see scheme; TON=turnover number).

Direct synthesis of quinazolinones by acceptorless dehydrogenative coupling of o-aminobenzamide and alcohols by heterogeneous Pt catalysts

HBEA zeolite-supported Pt metal nanoclusters (Pt/HBEA) effectively catalyze direct dehydrogenative synthesis of quinazolinones from o-aminobenzamide and alcohols under promoter-free conditions. This is the first heterogeneous catalytic system for this reaction, which has a turnover number (TON) more than 25 times higher than previous homogeneous catalysts as well as wide scope for aliphatic and aromatic alcohols.

C-3 alkylation of oxindole with alcohols by Pt/CeO2 catalyst in additive-free conditions

In a series of transition metal-loaded CeO2 catalysts and Pt-loaded catalysts on various supports, Pt-loaded CeO2 shows the highest activity for the selective C-3 alkylation of oxindole with octanol. The catalyst is effective for alkylation of oxindole and N-substituted oxindole with a series of substituted benzyl, linear, hetero-aryl alcohols under additive-free conditions and is recyclable. Our results demonstrate the first additive-free catalytic system for this reaction. Mechanistic studies show that this system is driven by the borrowing-hydrogen pathway. Structure–activity relationship studies show that co-presence of surface Pt0 species on Pt metal clusters and basic support is indispensable for this catalytic system.

Acceptorless dehydrogenative coupling of primary alcohols to esters by heterogeneous Pt catalysts

Supported platinum catalysts have been studied for the acceptor-free dehydrogenative coupling of primary alcohols to esters in the liquid phase under solvent-free conditions in N2 at 180 °C. The activity depends on the support material, and Pt-loaded SnO2 (Pt/SnO2) gives the highest activity. Pt/SnO2 shows higher activity than various transition metals (Ir, Re, Ru, Rh, Pd, Ag, Co, Ni, Cu) loaded on SnO2. The Pt/SnO2 catalyst (1 mol%) selectively converted various primary alcohols to their corresponding esters in moderate to high isolated yield (53–91%). This is the first example of reusable heterogeneous catalysts for the acceptor-free dehydrogenative coupling of primary alcohols to esters under additive-free and solvent-free conditions. Mechanistic and infrared (IR) studies are also shown to discuss the reaction pathway and a possible role of the SnO2 support as Lewis acid sites that activate carbonyl groups of adsorbed aldehyde intermediates.

Versatile and Sustainable Synthesis of Cyclic Imides from Dicarboxylic Acids and Amines by Nb2O5 as a Base-Tolerant Heterogeneous Lewis Acid Catalyst

Catalytic condensation of dicarboxylics acid and amines without excess amount of activating reagents is the most atom-efficient but unprecedented synthetic method of cyclic imides. Here we present the first general catalytic method, proceeding selectively and efficiently in the presence of a commercial Nb2 O5 as a reusable and base-tolerant heterogeneous Lewis acid catalyst. The method is effective for the direct synthesis of pharmaceutically or industrially important cyclic imides, such as phensuximide, N-hydroxyphthalimide (NHPI), and unsubstituted cyclic imides from dicarboxylic acid or anhydrides with amines, hydroxylamine, or ammonia.