•Pt/15AS is active and selective for cinnamaldehyde hydrogenation.•Fe-doped Pt/15AS catalyst greatly enhances the catalytic performance.•The PtFe0.25/15AS catalyst furnishes the highest reaction rate of 13.93 mol gPt−1 h−1.•The PtFe0.25/Al2O3@SBA-15 catalyst affords 76.9% selectivity to cinnamyl alcohol.•The PtFe0.25/Al2O3@SBA-15 catalyst shows the highest TOF value of 1.54 s−1.Selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) was conducted over a series of FeOx-doped Pt catalysts supported on a 15 wt% Al2O3@SBA-15 composite (15AS). It was found that the addition of FeOx to the catalyst greatly improved its performance. With an optimal Fe/Pt molar ratio of 0.25, the PtFe0.25/15AS catalyst reached a maximum reaction rate (defined as moles of converted CAL per gram of Pt per hour) of 13.93 mol gPt−1 h−1 with 76.9% selectivity to COL. Additionally, the PtFe0.25/15AS catalyst afforded the highest TOF value (defined as moles of converted CAL per mole of Pt active sites per second) of 1.54 s−1. X-ray photoelectron spectroscopy analyses and H2 temperature-programmed reduction and CO diffuse-reflectance infrared Fourier-transformation spectroscopy studies reveal that there is strong interaction between Pt nanoparticles and Al2O3@SBA-15 composites and also between Pt and FeOx, resulting in Pt species with a positive charge being dominant in PtFe0.25/15AS catalysts. Therefore, Pt species with positive charges, together with FeOx species, are beneficial for preferential adsorption and activation of carbonyl bonds of CAL, so that the activity and selectivity to COL were improved by PtFex/15AS catalysts (x represents the Fe/Pt molar ratio).Download high-res image (138KB)Download full-size image

•Cu9-Alx-My (M=Mg, Ca, Ba or Sr) catalysts prepared by a deposition-precipitation method were applied for ethyl acetate hydrogenation to ethanol.•Cu9-Al0.5-Mg1.5 catalyst afforded 97.8% ethyl acetate conversion, 98% selectivity to ethanol and showed good lifetime during 210 h test.•The Cu+/Cu0 species, specific surface area, initial reduction temperature and metal dispersion played key roles in determining the performance.Cu9-Alx or Cu9-Alx-My (M = Mg, Ca, Ba or Sr) catalysts were prepared by a deposition-precipitation method, characterized by means of H2-TPR, XRD and N2 sorption, and applied for hydrogenation of ethyl acetate to ethanol in a fixed-bed reactor. The molar ratio of Cu/Al or Cu/Al/M and the reaction parameters were investigated thoroughly. As a result, the Cu9-Al0.5-Mg1.5 catalyst with higher specific surface area, lower initial reduction temperature and better metal dispersion furnished 97.8% ethyl acetate conversion with 98% selectivity to ethanol under optimal reaction conditions. Moreover, the Cu9-Al0.5-Mg1.5 catalyst also showed good lifetime and neither the activity nor selectivity decreased during 210 h test. Based on the characterization of the Cu9-Al0.5-Mg1.5 catalyst, the optimal Cu+/Cu0 proportion played a key role in determining the superior performance.Download high-res image (202KB)Download full-size image

TiO2 was coated onto mesoporous silica SBA-15 by hydrolysis of tetrabutyl titanate to prepare 15 wt% TiO2@SBA-15 composites (15TS). The 15TS composites retain the mesostructure of the SBA-15 host, and TiO2 was highly dispersed and uniformly coated. 5 wt% Pt nanoparticles supported on 15TS were employed for liquid-phase selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL). Compared with the Pt catalyst supported on pristine SBA-15, the Pt/15TS catalyst afforded higher activity and selectivity to COL. Furthermore, the modification of the Pt/15TS catalyst by FeOx can greatly improve the activity and selectivity to COL. As a result, the Pt–FeOx/15TS catalyst displayed excellent selectivity to COL (around 84.5%) at nearly complete CAL conversion. Of particular note is that further calcination of the Pt–FeOx/15TS catalyst precursor in air at 773 K before reduction would greatly enhance the catalytic performance. Consequently, the TOF reached 3.06 s−1 with a selectivity to COL of 86.4% over the Pt–FeOx/15TS-773 catalyst. Moreover, the Pt–FeOx/15TS-773 catalyst can also be reused about eight times without distinct loss in activity or selectivity. Based on characterization by XPS and H2-TPR, the important promotion effect of FeOx and strong metal–support interaction played key roles in preferential adsorption and activation of CO bonds in CAL.

At near ambient temperature, Ru nanoparticles entrapped in ordered mesoporous carbons (OMCs) CMK-3 show superior efficiency in the green reduction process of nitrobenzene and its derivatives with hydrazine monohydrate as a hydrogen donor using water as solvent. The Ru/CMK-3 catalyst exhibited much higher activity than a commercial Ru/C catalyst purchased from Alfa Aesar toward the reduction of nitrobenzene with hydrazine monohydrate under the same conditions. The interaction of Ru nanoparticles with CMK-3 and the mesoporous structure of CMK-3 OMCs might play important roles in determining the catalytic performance of the Ru/CMK-3 catalyst. In addition, the catalytic performance of the Ru/CMK-3 catalyst for the reduction of nitrobenzene was also compared using different hydrogen sources. Hydrazine monohydrate was found to be suitable as a hydrogen donor for the reduction of nitrobenzene and its derivatives. Compared with those obtained in the reduction of nitrobenzenes using 4.0 MPa hydrogen, the catalytic activity of the Ru/CMK-3 catalyst obtained using hydrazine monohydrate as hydrogen donor was much higher in most cases.

•Hydrogenation of benzaldehyde, nitrobenzene and derivatives with Pt catalysts.•Pt/MIL-101 was more efficient than Pt/Al2O3@SBA-15 in water for these reactions.•The TOF obtained with Pt/Al2O3@SBA-15 was less than a half of that with Pt/MIL-101.•High hydrophobicity of MIL-101 can enrich substrates around Pt/MIL-101 catalyst.Metal organic-framework MIL-101 and inorganic mesoporous composites Al2O3@SBA-15 supported Pt catalysts, Pt/MIL-101 and Pt/Al2O3@SBA-15 catalysts, were prepared and characterized by means of X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), CO chemisorption and thermo-gravimetric (TG) analysis. Pt nanoparticles were highly dispersed on both supports. In liquid-phase hydrogenation of nitrobenzene, benzaldehyde and their derivatives, the Pt/MIL-101 catalyst was superior to the Pt/Al2O3@SBA-15 catalyst in water. For liquid-phase hydrogenation of nitrobenzene with the Pt/MIL-101 catalyst, owing to high solubility of nitrobenzene in ethanol, the reaction in ethanol went much faster than that in water, furnishing a turnover frequency (TOF) in ethanol up to 18,053 h−1, almost triple of that obtained in water under similar conditions. The highest TOF of 25,438 h−1 was obtained in ethanol for hydrogenation of 3-chloro-nitrobenzene with the Pt/MIL-101 catalyst. As for hydrogenation of benzaldehyde series, 2-fluoro-benzaldehyde and 3-fluoro-benzaldehyde gave the highest TOFs of 5146 h−1 and 3165 h−1 in water with the Pt/MIL-101 and Pt/Al2O3@SBA-15 catalysts, respectively. We deduce that surface property of MIL-101 with high hydrophobicity is helpful to enrich reactants around the Pt/MIL-101 catalyst in water, where nitrobenzene or benzaldehyde and its derivatives have a limited solubility, so that high catalytic performance was achieved with the Pt/MIL-101 catalyst in water. Of particular note is that the Pt/MIL-101 catalyst can be reused at least four times without loss in activity or selectivity.

Ru nanoparticles entrapped in ordered mesoporous carbons (CMK-3) served as an efficient and reusable catalyst for liquid-phase hydrogenation of benzaldehyde and its derivatives under our tested conditions (medium hydrogen pressure, room temperature, water as solvent). The Ru nanoparticles can be well stabilized by CMK-3 ordered mesoporous carbons so that the Ru leaching was below the detection limit of ICP-AES. Therefore, the Ru/CMK-3 catalyst can be used for at least five times without distinct loss in activity or selectivity for the hydrogenation of benzaldehyde. It is worthy of note that the Ru/CMK-3 catalyst was more efficient than the commercial Ru/C and homemade Ru/AC catalyst for the liquid-phase hydrogenation of benzaldehyde. The Ru/CMK-3 catalyst can also catalyze the liquid-phase hydrogenation of nitrobenzene and its derivatives with high conversions and excellent selectivities under optimal conditions.

Trimodal hierarchical yolk–shell materials consisting of TS-1 core and mesoporous carbon shell (YS-TS-1@MC) was successfully synthesized by using TS-1@mesosilica as hard template, sucrose as carbon source and organic base tetrapropylammonium hydroxide (TPAOH) as silica etching agent. The resultant YS-TS-1@MC contains the micropores (0.51 nm) in TS-1 core, the mesopores (2.9 nm) in carbon shell as well as a void or a stack pore between TS-1 fragements (TS-1 intercrystal mesopores, ∼18.4 nm). Under the rigorous etching conditions, the crystalline structure of TS-1core was well retained. The YS-TS-1@MC served as a good support for palladium nano-particles (Pd NPs) or Rh(OH)x species, giving rise to efficient bifunctional catalysts for the tandem reactions including one-pot synthesis of propylene oxide or amides.Yolk–shell material TS-1@MC with a trimodal hierarchical pore structure was successfully prepared and applied to support Pd nanoparticles or Rh(OH)x species, giving rise to novel bifunctional catalysts for tandem reactions.

•MIL-101 metal–organic frameworks as support for Pt nanoparticles.•Catalysts are effective for heterogeneous asymmetric hydrogenation of α-ketoesters.•Catalysts can be reused several times without distinct loss in activity or ee value.•Pt nanoparticles can be well stabilized by MIL-101 metal–organic frameworks.Pt/MIL-101 catalyst was prepared via a facile impregnation method and was tested for the chiral hydrogenation of α-ketoesters after chirally modified with cinchona alkaloid. The powder XRD, N2 adsorption–desorption, TEM, and CO chemisorption were employed to characterize the Pt/MIL-101 catalyst. The Pt/MIL-101 catalyst was proved effective for the asymmetric hydrogenation of ethyl pyruvate and ethyl 2-oxo-4-phenylbutyrate after chirally modified with cinchonidine. Up to 4469 h−1 TOF with 76.5% ee of (R)-(+)-ethyl lactate was obtained with the cinchonidine-modified Pt/MIL-101 catalyst in acetic acid. The fastest chiral hydrogenation of ethyl pyruvate with the cinchonidine-modified Pt/MIl-101 catalyst took place in neat water with medium enantioselectivity. While for the chiral hydrogenation of ethyl 2-oxo-4-phenylbutyrate with the cinchonidine-modified Pt/MIL-101 catalyst, over 2000 h−1 TOF with 76.8% ee value was achieved in a mixed solvent containing acetic acid and ethanol with an equal volume. Of particular note is that the Pt/MIl-101 catalyst could be reused at least four times without distinct loss in activity or enantioselectivity with addition of fresh chiral modifier each time in the chiral hydrogenation of ethyl pyruvate. The catalytic performance of Pt/MIL-101 catalyst was also compared for the chiral hydrogenation of ethyl pyruvate with the commercial Pt/C and Pt/Al2O3 catalysts after modification with cinchona alkaloid.

Pt nanoparticles supported on CMK-8 ordered mesoporous carbons (OMCs) with Ia3d symmetry after chirally modified with cinchonidine (CD) proved to be highly efficient for asymmetric hydrogenation of α-ketoesters. Up to 34,819 h−1 TOF with 75 % ee was furnished for the enantioselective hydrogenation of ethyl 2-oxo-4-phenylbutyrate with CD-modified Pt/CMK-8 catalyst. To the best of our knowledge, these results obtained with chirally modified Pt/CMK-8 catalyst are the best ones among those with Pt catalysts supported on carbon materials. It is suggested that both the physical structure features of CMK-8 OMCs and the chemical nature of Pt catalyst are beneficial for the asymmetric hydrogenation.

Pt nanoparticles entrapped in CMK-3 ordered mesoporous carbon materials, prepared by a facile impregnation method, were found to be efficient for the enantioselective hydrogenation of α-ketoesters by modification with cinchona alkaloids. The initial activity of higher than 23,000 h−1 TOF and 82% ee were obtained for the chiral hydrogenation of ethyl pyruvate with cinchonidine (CD)-modified Pt/CMK-3 catalyst. With regard to the chiral hydrogenation of ethyl 2-oxo-4-phenylbutyrate, the CD-modified Pt/CMK-3 catalyst afforded the highest TOF of 5615 h−1 and 64% ee. For comparison, commercially available Pt/C and Pt/Al2O3 catalysts were investigated as well. The Pt/CMK-3 catalysts were more efficient than the commercial Pt/C catalyst. Of particular note is that the Pt/CMK-3 catalyst exhibited good stability; only below 0.005% Pt atoms were leached into solution after the chiral hydrogenation of ethyl pyruvate in acetic acid, while the Pt leaching amount for the commercial Pt/Al2O3 and Pt/C catalysts was 0.15% and 0.25%, respectively. In addition, the Pt/CMK-3 catalyst could also be reused for more than 5 times without distinct loss of activity and enantioselectivity, while the reusability for the commercial Pt/C and Pt/Al2O3 catalysts was poor. Based on IR and Raman spectroscopic characterization, it is suggested that both the physical structure features, including high specific surface area, adequate pore volume, ordered mesopores and small Pt particle size with high dispersion, and the chemical nature of catalyst surface with high electron density would improve the performance of Pt/CMK-3 catalysts.Graphical abstractHighlights► CMK-3 ordered mesoporous carbon as support for Pt nanoparticles. ► Catalysts are effective for heterogeneous asymmetric hydrogenation of α-ketoesters. ► Catalysts are more efficient than the commercial Pt/C catalyst. ► Catalysts show superior stability to the commercial Pt/Al2O3 catalyst.

Ordered Ru-containing mesoporous polymers/silica (xRu-MPS) was for the first time successfully synthesized via a one-pot method. Characterization results demonstrated that the xRu-MPS samples had ordered meso-structure and Ru nanoparticles were highly dispersed on/inside the mesoporous polymer/silica. The xRu-MPS catalysts were proved to be efficient for the hydrogenation of benzaldehyde and its derivatives. When the Ru loading reached up to 4.8 wt%, the conversion of benzaldehyde could arrive 96% with 97% selectivity to benzyl alcohol. The 4.8Ru-MPS catalyst can also catalyze the hydrogenation of a series of benzaldehyde derivatives with different substituents at the phenyl ring with high performance. The results are quite comparable with those obtained on mesopolymer supported Ru catalyst prepared by a traditional impregnation method.

Platinum nanoparticles supported on periodic mesoporous resols by simple impregnation serve as effective, robust and remarkably reusable catalysts after chirally modified with cinchonidine for the asymmetric hydrogenation of ethyl pyruvate, affording up to 62% enantiomeric excess (ee) and a constant activity after 25th re-use. They can also catalyze the reaction in an environmentally benign manner by using water as a solvent.

A series of TiO2@SBA-15 composites with different TiO2 loadings have been synthesized through hydrolysis of tetrabutyl orthotitanate via a facile sol–gel method in the presence of SBA-15 mesoporous silica. The TiO2@SBA-15 composites retain the mesostructure of the SBA-15 host, and TiO2 is highly dispersed and uniformly coated. The TiO2@SBA-15 composites serve as remarkable supports for Pt nanoparticles, which can be applied efficiently to the liquid-phase hydrogenation of benzaldehyde, its derivatives, and other unsaturated compounds under mild conditions. Of particular note is that the Pt/TiO2@SBA-15 catalysts can be reused several times without distinct loss in activity or selectivity. The more electron-deficient surface state, together with the structural and physicochemical features of Pt/TiO2@SBA-15 catalysts, would improve the catalytic activity and reusability toward the liquid-phase hydrogenation of unsaturated compounds.Graphical abstractThe TiO2@SBA-15 composites serve as remarkable supports for Pt nanoparticles, which were proved active, selective and recyclable for the liquid-phase hydrogenation of benzaldehyde under mild conditions. The more electron-deficient surface state, together with the structural and physicochemical features of Pt/TiO2@SBA-15 catalysts, would improve the catalytic activity and reusability toward the liquid-phase hydrogenation of unsaturated compounds.Download high-res image (134KB)Download full-size imageHighlights► TiO2@SBA-15 composites with different TiO2 loadings as support for Pt nanoparticles. ► Pt/TiO2@SBA-15 catalyst is effective for liquid-phase hydrogenation of benzaldehyde. ► Catalysts are more efficient than the Pt/TiO2 catalyst under mild conditions. ► Catalysts can be reused for several times in water for benzaldehyde hydrogenation. ► Catalysts are also active for the hydrogenation of other unsaturated compounds.