We examined the formation mechanism of active sites on Cu/ZrO2 specific toward CO2-to-methanol hydrogenation. The active sites on Cu/a-ZrO2 (a-: amorphous) were more suitable for CO2-to-methanol hydrogenation than those on Cu/t-ZrO2 (t-: tetragonal) and Cu/m-ZrO2 (m-: monoclinic). When a-ZrO2 was impregnated with a Cu­(NO3)2·3H2O solution and then calcined under air, most of the Cu species entered a-ZrO2, leading to the formation of a Cu–Zr mixed oxide (Cu a Zr1‑a O b ). The H2 reduction of the thus-formed Cu a Zr1‑a O b led to the formation of Cu nanoparticles on a-ZrO2, which can be dedicated to CO2-to-methanol hydrogenation. We concluded that the selective synthesis of Cu a Zr1‑a O b , especially amorphous Cu a Zr1‑a O b , is a key feature of the catalyst preparation. The preparation conditions of the amorphous Cu a Zr1‑a O b specific toward CO2-to-methanol hydrogenation is as follows: (i) Cu­(NO3)2·3H2O/a-ZrO2 is calcined at low temperature (350 °C in this study) and (ii) the Cu loading is low (6 and 8 wt % in this study). Via these preparation conditions, the characteristics of a-ZrO2 for the catalysts remained unchanged during the reaction at 230 °C. The latter preparation condition is related to the solubility limit of Cu species in a-ZrO2. Accordingly, we obtained the amorphous Cu a Zr1‑a O b without forming crystalline CuO particles.

This paper reports the synthesis of primary amines from alcohols and NH3 by an Al2O3-supported Ni nanoparticle catalyst as the first example of heterogeneous and noble-metal-free catalytic system for this reaction without additional hydrogen sources under relatively mild conditions. Various aliphatic alcohols are tolerated, and turnover numbers were higher than those of Ru-based homogeneous catalysts. The catalyst was recoverable and was reused. The effects of the Ni oxidation states and the acid–base nature of support oxides on the catalytic activity are studied. It is clarified that the surface metallic Ni sites are the catalytically active species, and the copresence of acidic and basic sites on the support surface is also indispensable for this catalytic system.

Supported platinum catalysts have been studied for the reductive amination of levulinic acid (LA) by H2 to N-alkyl-5-methyl-2-pyrrolidones under solvent-free conditions. The activity depends on the type of metal (Pt, Re, Pd, Rh, Ru, Cu, Ni), support material, and coloaded oxides of transition metals (V, Cr, Mo, W, Re). In 24 kinds of catalyst tested, Pt and MoO X (molybdenum oxide) coloaded TiO2 (Pt-MoO X /TiO2) shows the highest activity. Pt-MoO X /TiO2 is effective for reductive amination of LA with wide varieties of amines under mild conditions (3 bar of H2, 100 °C, solvent-free) to give high isolated yield of pyrrolidinones and shows higher turnover number (TON) than previously reported catalysts for reductive amination of LA with an aliphatic amine. The catalyst can be separated from the reaction mixture by filtration, and the recovered catalyst can be reused. This is the first general and reusable heterogeneous catalytic system for the reductive amination of LA. On the basis of mechanistic studies, high activity of Pt-MoO X /TiO2 can be attributed to acid–base interaction between the acid sites of Pt-MoO X /TiO2 and carboxyl groups in LA and an intermediate.

Nickel nanoparticles loaded onto various supports (Ni/ MO x ) have been prepared and studied for the N-alkylation of amines with alcohols. Among the catalysts, Ni/θ-Al 2 O 3 prepared by in situ H 2reduction of NiO/θ-Al 2 O 3 shows the highest activity, and it acts as reusable heterogeneous catalyst for the alkylation of anilines and aliphatic amines with various alcohols (benzyl and aliphatic alcohols) under additive free conditions. Primary amines are converted into secondary amines and secondary amines into tertiary amines. For the reaction of aniline with an aliphatic alcohol the catalyst shows higher turnover number (TON) than precious metal-based state-of-the-art catalysts. Mechanistic studies suggest that the reaction proceeds through a hydrogen-borrowing mechanism. The activity of Ni catalysts depends on the nature of support materials; acid−base bifunctional supports give higher activity than basic or acidic supports, indicating that acid−base sites on supports are necessary. The presence of basic (pyridine) or acidic (acetic acid) additive in the solution decreased the activity of Ni/θ-Al 2 O 3 , which suggests the cooperation of the acid− base site of θ-Al 2 O 3 . For a series of Ni/θ-Al 2 O 3 catalysts with different particle size, the turnover frequency (TOF) per surface Ni increases with decreasing Ni mean particle size, indicating that low-coordinated Ni species and/or metal−support interface are active sites. From these results, we propose that the active site for this reaction is metal−support interface, where low-coordinated Ni 0 atoms are adjacent to the acid−base sites of alumina.

The selective catalytic reduction of NO with ammonia (NH3−SCR) catalyzed by Cu−CHA zeolites is thoroughly investigated using in situ spectroscopic experiments combined with on‐line mass spectroscopy (MS) under steady‐state NH3−SCR conditions and transient conditions for Cu(II)/Cu(I) redox cycles. Quantitative analysis of the in situ XANES spectra of Cu−CHA under steady‐state conditions of NH3−SCR show that NH3‐coordinated Cu(II) species is the dominant Cu species at low temperatures (100–150 °C). At higher temperatures, Cu(II) species and [Cu(NH3)2]+ complex coexist, possibly because the rate of the Cu(II)→Cu(I) reduction step is comparable to that of the Cu(I)→Cu(II) oxidation step. In situ XANES, IR/MS, and UV‐vis/MS experiments on the reduction half cycle demonstrate that the reduction of Cu(II) species occurs via the reaction of NH3‐liganded Cu(II) with NO to yield N2 and H2O. For the oxidation half cycle, in situ XANES experiments of Cu(I) oxidation in 10 % O2 at 200 °C indicate that an increased density in CHA zeolite exhibits a higher oxidation rate. In situ UV‐vis experiments of Cu(I) reoxidation using different mixtures of oxidant feed gas demonstrate the key role of O2 in the oxidation cycle. It is suggested that the reoxidation of Cu(I) to Cu(II) species occurs with only O2 as the oxidant, and a high Cu density in CHA zeolite promotes SCR activity by enhancing the oxidative activation of Cu(I) to Cu(II) during the catalytic cycle.

Pt/Nb2O5 shows more than 60 times higher TON than non-SMSI Pt catalysts and previous catalysts for the hydrodeoxygenation of stearic acid to n-octadecane at 180 °C in 8 bar H2. Nb2O5 can act as an activation site of carbonyl groups.

Ni–MoOx/C showed more than 300 times higher TON than previously reported noble metal-free catalysts for the title reaction.

Valeric acid and valeric biofuels are obtained in high yield by direct hydrogenation of levulinic acid catalyzed by Pt/HMFI under relatively mild conditions (2 or 8 bar H2, 200 °C), driven by cooperation of the metal and support Brønsted acid sites.