Weiwei Lin

Highly selective Pt/ordered mesoporous TiO2–SiO2 catalysts for hydrogenation of cinnamaldehyde: The promoting role of Ti2+

A highly selective and stable catalyst based on Pt nanoparticles confined in Mesoporous TiO2-SiO2 frameworks were prepared and employed for selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. The as-prepared Pt/MesoTiO2-SiO2-M catalyst displayed excellent selectivity to cinnamyl alcohol (around 91%) at nearly complete conversion. Ti(2+) and stronger metal-support interaction (SMSI) played key roles on the adsorption behavior of cinnamaldehyde and activation of CO bonds. The existence of amorphous SiO2 and mixed TiO2 phases (anatase and rutile) was helpful for the formation of Ti(2+) sites and SMSI. The electron-enriched Pt surfaces and the formed Pt-TiOx system benefited the enhanced activity and selectivity.

Supported polyethylene glycol stabilized platinum nanoparticles for chemoselective hydrogenation of halonitrobenzenes in scCO2.

Polyethylene glycol stabilized platinum nanoparticles were immobilized on solid supports such as γ-Al2O3, SBA-15, TiO2 and active carbon, forming supported polyethylene glycol stabilized platinum nanoparticles (SPPNs). In the hydrogenation of p-chloronitrobenzene (p-CNB) in supercritical carbon dioxide (scCO2), the SPPN showed high selectivity to p-chloroaniline (>99.3%) in the whole range of conversion. Such high selectivity to corresponding haloanilines (HANs) (>99.1%) was also obtained in the hydrogenation of o-CNB, m-CNB, 2-chloro-6-nitrotoluene, p-bromonitrobenzene and m-iodonitrobenzene. The dehalogenation and the accumulation of intermediates were fully inhibited simultaneously in scCO2. The SPPN catalysts could be reused several times without loss of high selectivity in present reaction system.

Hydrogenation of levulinic acid by RuCl2(PPh3)3 in supercritical CO2: the significance of structural changes of Ru complexes via interaction with CO2

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was studied with a homogeneous RuCl2(PPh3)3 catalyst in supercritical CO2 (scCO2). The conversion of LA was observed to increase with CO2 pressure and the possible reasons for this rate acceleration were discussed, including the molecular interactions of CO2 with the reacting and catalytic species as well as the acidity and phase behavior of the reaction mixture. The interaction between CO2 and RuCl2(PPh3)3 was significant, which resulted in the production of an active RuHCl(CO)(PPh3)3 complex and thus enhanced the rate of hydrogenation in the presence of CO2.

Selective hydrogenation of o-chloronitrobenzene over anatase-ferric oxides supported Ir nanocomposite catalyst

The catalytic performance of Ir/TiO2-FeOx, an Ir/TiO2 catalyst modified with FeOx, was investigated for the hydrogenation of o-chloronitrobenzene, FeOx was found to promote both the activity and selectivity significantly. The initial reaction rate of Ir/TiO2-FeOx(10) nanocomposite catalyst was four times as high as that of Ir/TiO2 catalyst. Especially, the accumulation of intermediates was prohibited and finally 100% selectivity to o-chloroaniline was obtained at 100% conversion. Herein, we mainly discussed the promoting effect of FeOx with using the results of powder X-ray diffraction, transmission electron microscopy, element analysis mapping, hydrogen-temperature programmed reduction, hydrogen-temperature programmed desorption, diffuse reflectance infrared fourier transform spectra and X-ray photoelectron spectroscopy analysis. The FeOx was highly dispersed and a portion of FeO species existed in the Ir/TiO2-FeOx nanocomposite catalyst. Moreover, the FeOx was certified to have a strong interaction with Ir species, which should contribute to the excellent performance of the Ir/TiO2-FeOx nanocomposite catalyst.

Metal-free catalytic conversion of CO2 and glycerol to glycerol carbonate

Using CO2 as a carbonyl building block to synthesize valuable chemicals is an important issue in the field of green and sustainable chemistry. Herein, the conversion of CO2 with glycerol to glycerol carbonate was investigated in the presence of 2-cyanopyridine. It was found that 2-cyanopyridine not only acts as the dehydrating agent to break the thermodynamic limit of the reaction, but also activates the carbonyl bond of CO2 to catalyze the present carbonylation as confirmed by FTIR experimental spectra. Moreover, the activation closely depends on the stereo-structure of cyanopyridine, in that 3-cyanopyridine and 4-cyanopyridine do not have such activating function. The theoretical calculation demonstrated that 2-cyanopyridine could bond CO2 through the conjugating nitrogen to form a five-membered ring, thus CO2 is activated and then reacts with glycerol to produce glycerol carbonate. The reaction parameters were examined and evaluated for the reaction catalyzed with 2-cyanopyridine in the absence of any metal catalysts and additives. With increasing CO2 pressure, the yield of glycerol carbonate increases, and under the optimum conditions an 18.7% yield is obtained which is one of the best results reported up to now. The present work provides a new way for activation of CO2.

PdGa/TiO2 an efficient heterogeneous catalyst for direct methylation of N-methylaniline with CO2/H2

An effective sustainable heterogeneous PdGa/TiO2 catalyst was prepared for direct methylation of N-methylaniline with CO2/H2 to N,N-dimethylaniline. The PdGa/TiO2 catalyst exhibited 98% conversion and 94% selectivity under the reaction conditions (180 °C, 5 MPa H2, 5 MPa CO2, 10 h), which are one of the best results reported to date for the heterogeneous N-methylation with CO2 as methylation reagent over the supported metal catalysts. The PdGa/TiO2 catalyst was well characterized using TEM, TPR, XPS, CO-adsorption IR studies and high-pressure in situ FTIR studies. It was confirmed that PdGa bimetallic alloy nanoparticles were formed and highly dispersed on the TiO2 support, and the electron-deficient Pd derived from the interaction with Ga could activate CO2 and transform it to formic acid, which is the key step for the discussed methylation, and high activity was obtained over the PdGa/TiO2 catalyst. The activating properties of the PdGa/TiO2 catalyst will open a new route for transfer and utilization of CO2 in the fields of energy and environmental fields.

A stable and active AgxS crystal preparation and its performance as photocatalyst

Abstract Ag x S crystals were synthesized via hydrothermal (Ag x S- H ) and in situ ion-exchange (Ag x S- IE ) methods. The samples were characterized by scanning electron microscopy, X-ray diffraction, ultraviolet-visible-near infrared absorption spectroscopy, N 2 adsorption-desorption, X-ray photoelectron spectroscopy and surface photovoltage measurements. The photocatalytic performance was investigated for the decomposition of methyl blue (MB) under visible light irradiation ( λ ≥ 420 nm). The Ag x S- H had smaller particles, wider band gap and weaker recombination of photoinduced charges than Ag x S- IE , resulting in a higher photocatalytic activity. Moreover, Ag x S- H was stable, and could be reused five times without loss of photocatalytic activity. Additionally, a possible pathway for the photocatalytic degradation of MB over Ag x S has been proposed, that MB was oxidized mainly by hydroxyl radicals and partly via electron holes generated in the Ag x S. Ag x S- H is an efficient photocatalyst and has great potential for the degradation of harmful organic dyes in wastewater.

A Study on the Oxygen Vacancies in ZnPd/ZnO-Al and their Promoting Role in Glycerol Hydrogenolysis

The relationship between catalyst structure and catalytic activity is an important and challenging topic for researchers in the field of catalysis. In this work, the effect of oxygen vacancies on the activity of ZnPd/ZnO‐Al catalysts was studied in an important reaction—glycerol hydrogenolysis. Interestingly, the catalytic activity improved significantly with the addition of a small amount of Al, and high selectivity to 1,2‐propanediol (>90 %) was achieved in glycerol hydrogenolysis over ZnPd/ZnO‐Al catalysts. Importantly, the formation of oxygen vacancies benefits from the substitution of Al atoms, and the Al content in the ZnO lattice is related to the oxygen vacancies density and catalytic activity. Moreover, the important role played by oxygen vacancies in glycerol hydrogenolysis has been discussed in detail.

Solvent effects on heterogeneous catalysis in the selective hydrogenation of cinnamaldehyde over a conventional Pd/C catalyst

Solvent effects in the selective hydrogenation of an α,β-unsaturated aldehyde of cinnamaldehyde (CAL) were investigated under gas–liquid–solid reaction conditions. A conventional 5 wt% Pd/C catalyst and twelve organic solvents were used, including apolar solvents (three) and protic (two) and aprotic (seven) polar ones. The total rate of CAL hydrogenation strongly depended on the solvents used. The relationship between the rate of CAL hydrogenation observed and a few different solvent parameters was examined. The main product was hydrocinnamaldehyde (HCAL) with a selectivity of 80% or higher in most of the solvents examined except for pyridine and 4-methylpyridine. In these two solvents, the CAL hydrogenation was slow and the main product was changed to cinnamyl alcohol (COL) with a selectivity of about 60%. The addition of a small volume of pyridine to other solvents such as 2-propanol and tetrahydrofuran could change the rate of hydrogenation and switch the main product from HCAL to COL. Possible interactions among the solvents, CAL substrate, and Pd/C catalyst were examined by FTIR (attenuated total reflection (ATR-) and diffuse reflectance modes (DR-)) and TPD to discuss the solvent effects observed in the Pd-catalyzed heterogeneous CAL hydrogenation.

A Robust Ru/ZSM-5 Hydrogenation Catalyst: Insights into the Resistances to Ruthenium Aggregation and Carbon Deposition

A long‐life topic in the field of heterogeneous catalysis has been to develop supported catalysts that are stable against the aggregation of active metal and carbon deposition. Herein, we report a highly stable Ru/ZSM‐5 catalyst for the hydrogenation of levulinic acid in water, which can be recycled at least 10 times without apparent loss of activity (conv. >95 %, yield >85 %). The influences of types of Al species, structure of support, Ru sizes, Ru leaching, and carbon deposition, etc. on activity and stability were discussed in detail. It was confirmed that the tetrahedral‐coordinated framework Al in ZSM‐5 contributed to the favorable metal–support interaction, and thus suppressed the aggregation and leaching of ruthenium during recycling. Besides, the suitable pore volume and channel network connectivity successfully prevent from deposition of carbonaceous residues.