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Herein, we report that Pd nanoparticles (NPs) anchored on graphitic nitride carbon (Pd/g-C3N4) catalysts with various Pd contents (1.55 wt%, 0.14 wt%, 0.04 wt%) are successfully prepared via a simple NaBH4 reduction method, exhibiting excellent catalytic activity and selectivity toward 4-aminophenol (4-AP) in 4-nitrophenol (4-NP) selective hydrogenation. 4-NP is completely converted to 4-AP (yield ∼ 100%) under quite moderate reaction conditions (40 °C, 2.0 MPa H2 and 5 min) over the 1.55 wt% Pd/g-C3N4 catalyst, with a high reaction rate r = 134.4 mol4-NP molPd−1 min−1. The excellent catalytic performance can be attributed to the following reasons: (1) a higher ratio of Pd(0)/Pdn+ provides much more exposed active sites for the potential adsorption and activation of the reactants, which is beneficial for increasing the reaction rate and catalytic activity; (2) Pd NPs are highly dispersed on g-C3N4 due to the strong interaction of Pd–N or Pd–C; (3) the interfacial synergism effect between Pd NPs and g-C3N4 enables the effective adsorption and activation of H2 (4-NP) at Pd (g-C3N4), promoting the catalytic hydrogenation of 4-NP and improving their catalytic properties. In addition, this catalyst has superior reusability. [ABSTRACT FROM AUTHOR]

Pd particles coated with ZIF-67 (Pd@ZIF-67) was prepared from the self-reduction of palladium acetate. With isopropanol as the solvent, the furfural hydrogenation reaction performances of Pd@ZIF-67 and ZIF-67 heated at different temperatures were tested in H2 and N2 reaction atmosphere, respectively. The pyrolytic carbonization of Pd@ZIF-67 and ZIF-67 produced Pd–Co@C and Co@C in carbon coating structures, respectively. It was found that furfural hydrogenation reaction systems with different catalytic active sites included direct hydrogenation with H2 as the hydrogen source, and transfer hydrogenation with isopropanol as the hydrogen donor. The Pd–Co@C and Co@C with metal active sites both experienced direct hydrogenation and transfer hydrogenation simultaneously, and the direct hydrogenation activity was higher. The ZIF-67 with Lewis acidic sites experienced transfer hydrogenation, and the catalytic activity was higher than the transfer hydrogenation activity of Pd–Co@C and Co@C. Moreover, reaction routes in which furfural direct hydrogenation and transfer hydrogenation occurred in metal active sites and Lewis acidic sites were identified. [ABSTRACT FROM AUTHOR]

The effect of supports (SiO2, ZnO, ZrO2 and Al2O3) on the hydrogenation and water-tolerance of copper catalysts were studied at reaction condition containing water. The copper catalysts with different supports showed different hydrogenation and water-tolerance performances. The result of XRD, BET, Raman, TPR, XPS, N2O titration and TEM confirmed the interactions between copper and supports, and the formation of Cu–MxOy (M = Zn, Zr, and Al) interfaces had great effects on the catalytic activity and water-tolerance performance. In particular, too strong interactions suppressed the reduction of copper oxides, resulting in a low catalytic activity. Nevertheless, the formation of Cu–MxOy could provide more active sites, which provided more chances for the reactants to touch the active sites. By this method, the loss of active sites due to competitive adsorption between water and ethyl acetate could be made up, so that the water-tolerance of copper catalysts was improved. [ABSTRACT FROM AUTHOR]

Synthesis of an easily separable and efficient catalyst is of great significance for selective hydrogenation of unsaturated functional groups. In this work, novel magnetic flower-like carbonaceous Pd catalysts are constructed for the selective reduction of the C＝C bond. According to the characterization results, a flower-like architecture is observed in the catalysts containing both Fe3O4 and Pd NPs, which is constructed by the secondary self-assembly in the preparation process due to the interaction between Pd and magnetic nitrogen-doped graphene (Fe3O4-NG). More flower-like structures are formed by increasing the Pd loading amount, further enhancing the specific surface area of the catalyst. The specific surface area of Pd-FONG-3 is the highest (521.17 m2 g−1). Combining the results of characterization and experiments, it is found that the catalytic activity is positively related to the flower-like architecture and the interaction between Pd NPs (6.0 nm) and Fe3O4 NPs (6.7 nm). Fe3O4 is not only beneficial to the magnetic recovery of the catalyst, but also acts as a cocatalyst, which can significantly improve the reactant conversion. Moreover, N species play an important role in protecting the C＝O bond, resulting in the selective hydrogenation of the C＝C group. Herein, Pd-FONG-3 exhibits excellent activity in the selective hydrogenation of cinnamaldehyde (CAL) with 99.5% conversion and 96.5% hydrocinnamaldehyde (HCAL) selectivity, and its catalytic performance is much better than that of the commercial 5% Pd/C catalyst (100% conversion and 69.1% HCAL selectivity). This work provides a new strategy to construct highly active catalysts with magnetic recovery properties for selective hydrogenation of C＝C bonds, and Pd-FONG-3 shows tremendous application foreground. [ABSTRACT FROM AUTHOR]

The effects of the ZnO/SiO2 ratio on the water tolerance of Cu/SiO2 and Cu/ZnO catalysts were studied by ethyl acetate with 5 wt% water hydrogenation. Notably, the addition of an appropriate amount of ZnO endows Cu/SiO2 catalysts with satisfactory water-tolerant hydrogenation performance by a decrease in the reaction temperature without sacrificing conversion. At the same time, agglomeration can be alleviated for Cu/ZnO catalysts due to the optimal addition of SiO2, which is considered as a partition material that effectively hinders the agglomeration of the Cu/ZnO catalyst. However, the addition of ZnO was not favourable for the copper dispersion of Cu/SiO2. The stability of Cu/SiO2 catalyst quickly degraded due to excessive ZnO being introduced by sintering. The copper dispersion of Cu/ZnO catalysts initially increased with increasing SiO2 content, but then decreased. The addition of excess SiO2 also led to decreased activity and rapid deactivation of the Cu/ZnO catalyst. In our study, the appropriate addition of ZnO (5 wt%) and SiO2 (5 wt%) had a positive effect on the Cu/SiO2 and Cu/ZnO catalysts, respectively. [ABSTRACT FROM AUTHOR]

Gamma valerolactone (GVL) is an important chemical feedstock from which several value-added fine chemicals, fuels and fuel additives are manufactured. GVL is the product obtained in the hydrogenation of levulinic acid (LA), which in turn is generally manufactured from several renewable resources such as pentoses and hexoses. The present work deals with the synthesis of SBA-15 and Sn loaded catalysts [x% Sn/Al-SBA-15 (x = Si/Sn = 10, 25, 50, 75 and 100 with Si/Al = 25)] using a hydrothermal in situ method. A variety of both bulk and surface characterization techniques such as XRD, FT-IR, BET, FE-SEM, HR-TEM, XPS, TGA/DTA and UV-DRS were used to characterize the bare and Sn/Al-SBA-15 catalysts. The characterization studies revealed the presence of Sn species well dispersed in the uniform pore channels of Al-SBA-15. All the synthesized catalysts were tested in the liquid-phase catalytic transfer hydrogenation of levulinic acid at atmospheric N2 pressure under mild reaction conditions. Among them, the Sn/Al-SBA-15 (Si/Sn = 25) catalyst showed remarkable conversion of levulinic acid (99%) and very high selectivity towards GVL (100%). The various reaction parameters such as metal loading, reaction temperature, reaction time and catalyst weight were optimized to get the maximum conversion of levulinic acid with high selectivity towards the desired product. The stability and reusability of the best catalysts were also tested up to five cycles and there was not much variation in the catalytic activity in terms of conversion. [ABSTRACT FROM AUTHOR]

The influence of Cu loading on the structural evolution and catalytic behavior in selective hydrogenation of dimethyl oxalate (DMO) by Mg2+ doped nanoscaled Cu–Mg/ZnO catalysts has been investigated. It is found that the accessible Cu0 surface area and ZnO dispersion increased gradually with the Cu loading increasing from 10.0 wt% to 40.0 wt%, and that the Cu and ZnO NP size distribution has a great effect on the chemical interaction between the Cu and ZnO phase, further determining the surface chemical properties of the catalysts. On the other hand, the catalytic behavior of the Cu–Mg/ZnO catalyst in DMO hydrogenation is closely related to the Cu loading introduced into the system. Most of all, the 30Cu–Mg/ZnO catalyst with 30 wt% Cu loading exhibits 100.0% DMO conversion and 98.0% ethylene glycol (EG) yield even under LHSV = 3.5 h−1, superior to those of the other catalysts. This excellent catalytic behavior should be attributed to the strengthened Cu–Zn synergistic effect and suppressed strong surface basic sites, originating from the enhanced Cu–ZnO interface area. Additionally, the correlation between catalytic activity and Cu species distribution suggests that the DMO dissociation on the Cu+ sites generated on the Cu–ZnO interface is the rate-determining step in the presence of enough exposed Cu0 sites over the Cu–Mg/ZnO catalysts. [ABSTRACT FROM AUTHOR]

A new type of Pd@mSiO2 composite nanospheres with controlled pore structure, consisting of internal Pd cores and controlled mesoporous silica shells, has been prepared by a facile one-pot method. The thickness and pore size of the shell could be easily tuned by changing the amounts of TEOS and the hydrophobic block length, respectively, during synthesis. In this perspective, the effects of CTAB concentration, pH, and TEOS concentration on the monodisperse sphere morphology of Pd@mSiO2 nanoparticles (NPs) were investigated. In addition, a nucleation mechanism was proposed. Hydrogenation of nitrobenzene to aniline was used as a model reaction to discuss the effect of pore size on the transport rate of the reactants and the product selectivity in metal-catalyzed hydrogenation. The catalysts exhibited a high conversion rate and significantly enhanced stability, leading to a higher recyclability without loss of catalytic activity compared to conventional supported catalysts and commercial catalysts. [ABSTRACT FROM AUTHOR]

A new catalyst was developed for selective hydrogenation of dioctyl phthalate (DOP) to produce the environmentally friendly plasticizer di(2-ethylhexyl)hexahydrophthalate (DEHHP) by incorporating rhodium via chemical fluid deposition into an aluminum-modified mesocellular foam (MCF). The Al-modified MCF containing a Si/Al molar ratio of 5 and 1 wt% Rh achieved 100% conversion of DOP to DEHHP with no side products at 80 °C and 68 atm H2 pressure in one hour reaction time. On the other hand, a 1 wt% Rh/MCF catalyst without any surface modification with Al yielded only 29% conversion. The interaction of Rh with the support became stronger when Al was incorporated onto the MCF support. An effective control of the acidity provided by Al by closely monitoring the Si/Al ratio was key in improving the catalytic activity of the Rh/Al-MCF catalysts. [ABSTRACT FROM AUTHOR]

Cu–ZrO2 catalysts were synthesized by the methanothermal (Me) and oxalate gel precipitation (Og) methods. Detailed characterization of the catalysts synthesized by the Me method shows that these contain only Cu substituted into the tetragonal ZrO2 lattice. For catalysts prepared using the Og method Cu is found not only in the tetragonal ZrO2 lattice but also in the form of CuO particles on the zirconia surface. When these materials were tested for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) it was found that Me materials show no catalytic activity, whereas GVL was formed using Og catalysts. A reduction treatment of the Og catalysts prior to use resulted in a marked increase in the catalytic activity, however, no activity increase was observed when the Me material was exposed to a similar treatment before testing. Based on these results and characterization data, we conclude that the catalytically active component of Cu–ZrO2 catalysts for the hydrogenation of LA is reduced Cu particles dispersed on the catalyst surface with strong interaction with the Cu incorporated zirconia support, while the role of Cu in the zirconia lattice is to improve the adhesion of these particles and maintain their dispersion. [ABSTRACT FROM AUTHOR]

A series of ruthenium(ii) complexes with three novel PNX-type pincer ligands is reported, in which X denotes a heterocyclic donor group (PNX = Ph2PCH2CH2N(H)CH2-X, X = 2-pyridyl, 2-furanyl, 2-thiophenyl or 2-pyrrolyl). The reaction of [(Ph3P)3RuCl2] with one equivalent of ligand leads to the trans-dichloro complexes [(PNX)RuCl2(PPh3)] (1–4) for all ligands, whereas the complexation of [(Ph3P)3Ru(H)(Cl)(CO)] results in different types of complexes. The variation of the heterocyclic donor group is in line with different binding properties and a labilization of this group. Investigations on the catalytic activity of different types of ruthenium(ii) complexes in hydrogenation and dehydrogenation reactions reveal that more labile bound heterocycle donors result in a decrease of catalytic productivity and activity. [ABSTRACT FROM AUTHOR]

The hydrogenation of carbon dioxide to methanol is perceived as an effective way to mitigate global warming and drive fossil-fuel companies towards sustainable energy sources. In this study, a series of Cu/ZnO–CeO2 catalysts were prepared by a co-precipitation method, and the effect of the CeO2 content on the catalytic performance of the Cu/ZnO–CeO2 catalysts for the hydrogenation of CO2 to CH3OH was analysed. The physicochemical properties of the catalysts were investigated using XRD, H2-TPR, CO2-TPD, BET, XPS, TEM, and DRIFTS. The CZC-3 catalyst (CZC stands for Cu/ZnO–CeO2 catalyst and 3 indicates a 30% CeO2 content) had the best catalytic activity at 280 °C in a 3 MPa CO2/H2 (1/3) atmosphere, exhibiting a CO2 conversion rate of 15.6% and a methanol yield of 10.06%. More dispersed CuO species and oxygen vacancies were detected on the CZC-3 catalyst, leading to good activation of H2 and CO2, respectively. In situ DRIFTS results for the catalysts showed that the hydrogenation of CO2 to methanol over Cu/ZnO–CeO2 catalysts occurs via the formate pathway. The CeO2-rich Cu/ZnO–CeO2 catalyst facilitated the conversion of formate to CH3OH, and the presence of a large number of intermediate species on the surface of the CZC-3 catalyst greatly contributed to its catalytic performance for CO2 hydrogenation. [ABSTRACT FROM AUTHOR]