Double Solvent Impregnation Research Articles

Efficient visible light initiated one-pot syntheses of secondary amines from nitro aromatics and benzyl alcohols over Pd@NH2-UiO-66(Zr)

Pd@NH2-UiO-66(Zr), with small-sized Pd nanoparticles encapsulated inside the cavities of NH2-UiO-66(Zr), was obtained via a double-solvent impregnation followed by a photoreduction process, which shows superior activity for the visible light initiated syntheses of secondary amines from nitro compounds and alcohols, via a sequential photocatalytic hydrogenation of nitro compounds/dehydrogenation of alcohols, condensation of amines and aldehydes to imines, and the hydrogenation of imines. Simultaneous consumption of photogenerated electrons/holes in the photocatalytic hydrogenation of nitro compounds to amines and dehydrogenation of alcohols to aldehydes promotes the whole reaction. Due to the confinement effect of the cavity and the small-sized Pd nanoparticles, Pd@NH2-UiO-66(Zr) shows significantly superior performance as compared with Pd/NH2-UiO-66(Zr), in which larger Pd nanoparticles are deposited on the surface. This study provides an efficient and green strategy for the production of secondary amines and highlights the great potential of using M/MOFs nanocomposites as multifunctional catalysts for light induced one-pot tandem reactions.

Highly active CuZn/SBA-15 catalyst for methanol dehydrogenation to methyl formate: Influence of ZnO promoter

• The catalytic performance of x CuZn/SBA-15 was dramatically superior to Cu/SBA-15. • The activity of x CuZn/SBA-15 in methanol dehydrogenation to MF was affected by ZnO amount. • The appropriate ZnO amount improved Cu dispersion and Cu 0 /(Cu 0 +Cu + ) ratio. • 10CuZn/SBA-15 exhibited most excellent activity along with favorable stability. Stable and efficient Cu/SBA-15 and x CuZn/SBA-15 ( x = 5, 10 and 15) in methanol dehydrogenation to methyl formate (MF) are prepared through a double-solvent impregnation (DI) method. Among all catalysts, 10CuZn/SBA-15 shows the highest catalytic performance with selectivity to MF about 88.1 % and methanol conversion of 31.1 %, which is attributed to the well-dispersed Cu particles and high ratio of Cu°/(Cu° + Cu + ). The proper amount of ZnO could improve dispersion of Cu because of its geometrical spacer, inhibiting growth of Cu particle, and the best dispersion is achieved in 10CuZn/SBA-15. Furthermore, the Cu°/(Cu° + Cu + ) ratio is greatly promoted with the assistance of ZnO, attributed to Cu-ZnO interaction, which reaches maxima of 53.3 % at a Cu/Zn mole ratio of 10. Specially, the optimized catalyst shows evident suitability at high temperature for methanol dehydrogenation reactions along with high level of conversion and selectivity for 100 h. Overall, our findings reveal that modification by the appropriate amount of ZnO in Cu-based catalyst has a positive impact on obtaining MF for the methanol dehydrogenation.

Bimetallic AgPd/UiO-66 Hybrid Catalysts for Propylene Glycol Oxidation into Lactic Acid.

Different methods (the wetness impregnation of Ag and Pd precursors dissolved in water or acetonitrile solution, and the double solvent impregnation technique) were employed to immobilize Ag–Pd nanoparticles (NPs) into the pores of the microporous zirconium-based metal-organic framework known as UiO-66. The obtained materials were characterized by using nitrogen adsorption-desorption at −196 °C, powder X-ray diffraction, UV-Vis diffusion reflectance spectroscopy, and transition electron microscopy measurements. Special attention was paid to the acid and redox properties of the obtained materials, which were studied by using temperature-programmed desorption of ammonia (TPD-NH3) and temperature-programmed reduction (TPR-H2) methods. The use of a drying procedure prior to reduction was found to result in metallic NPs which, most likely, formed on the external surface and were larger than corresponding voids of the metal-organic framework. The formation of Ag–Pd alloy or monometallic Ag and Pd depended on the nature of both metal precursors and the impregnation solvent used. Catalytic activity of the AgPd/UiO-66 materials in propylene glycol oxidation was found to be a result of synergistic interaction between the components in AgPd alloyed NPs immobilized in the pore space and on the external surface of UiO-66. The key factor for consistent transformation of propylene glycol into lactic acid was the proximity between redox and acid-base species.

Nitrogen and Oxygen Co-Doping Assisted Synthesis of Highly Dispersed Pd Nanoparticles on Hollow Carbon Spheres as Efficient Electrocatalysts for Oxygen Reduction Reaction.

Electrochemical reduction of O2 (oxygen reduction reaction; ORR) provides an opportunity to achieve the commercial application of clean energy, but it remains challenging, so the rational design of inexpensive and efficient electrocatalysts is required. Palladium-based electrocatalysts have emerged as a class of the most promising candidates for the ORR, which could accelerate O2 adsorption, dissociation, and electron transfer. However, the metal Pd atoms tend to aggregate into nanoparticles, driven by the tendency of the metal surface free energy to decrease, which significantly reduces the atom utilization efficiency and the catalytic performance. Herein, a facile double solvent impregnation method is developed for the synthesis of highly dispersed Pd nanoparticles supported on hollow carbon spheres (Pd-HCS), which could act as efficient electrocatalysts for the ORR in basic solution. Systematic investigation reveals that the nitrogen-containing and oxygen-containing functional groups (especially -COOH groups) are essential for achieving the homogenous dispersion of Pd nanoparticles. Significantly, the optimized Pd-HCS electrocatalyst with homogeneously dispersed Pd nanoparticles and Pd-N sites delivers high electrocatalytic activity for the ORR and excellent stability, without significant decay in onset potential and half-potential and good resistance to methanol crossover. This work offers a new route for the rational design of efficient ORR electrocatalysts toward advanced materials and emerging applications.

Efficient photocatalytic one-pot hydrogenation and N-alkylation of nitrobenzenes/benzonitriles with alcohols over Pd/MOFs: Effect of the crystal morphology & “quasi-MOF” structure

One-pot multi-step reactions over visible-light induced catalysis feature the sustainable green process. Here, ligand structure change and 2-MI coordinated modulation were adapted to adjust the crystal size, morphology and crystalline structure of Fe-MOFs; double solvent impregnation was employed for the Pd loading; “quasi-MOF” materials with retained morphology were formed with calcination under N2. Above modified materials were employed as multifunctional photocatalysts for highly efficient one-pot hydrogenation and N-alkylation of nitrobenzenes or benzonitriles with alcohols after in situ Pd photoreduction. Photocatalytic performance was evidently affected by the Fe-MOFs crystal size, morphology, crystalline structure alteration and “quasi-MOF” construction. One-pot hydrogenation and N-alkylation of benzonitriles with alcohols was achieved with excellent catalytic performance firstly in heteroegeneous catalysis. Reaction mechanism was proposed with the assistance of in situ DRIFTS.

Benzene hydrogenation over polydopamine-modified MCM-41 supported Ruthenium-Lanthanum catalyst

Polydopamine–modified MCM-41 was prepared by sodium periodate–induced polymerization. Ru–La supported on MCM-41 and polydopamine–modified MCM-41 catalysts were prepared by double solvent impregnation method and tested for benzene hydrogenation to cyclohexene. Polydopamine–modified MCM-41 supported Ru–La catalyst exhibits much higher hydrophilicity and more moderate catalytic activity than unmodified MCM-41 supported Ru–La catalyst. The higher hydrophilicity, more moderate catalytic activity, and long-range order of mesoporous structure are beneficial for improving cyclohexene selectivity on account of the promotion of the desorption and the inhibition of the adsorption of cyclohexene. 47.0% of cyclohexene yield was obtained over Ru–La supported on polydopamine–modified MCM-41 in benzene hydrogenation.

Nitrogen-doped porous carbon derived from ZIF-8 as a support of electrocatalyst for enhanced oxygen reduction reaction in acidic solution

The composites of platinum (Pt) nanoparticles (NPs) loaded on nitrogen-doped porous carbon (NPC) derived from ZIF-8 were successfully prepared based on double solvent impregnation and chemical reduction methods. By changing the calcination temperature and duration of ZIF-8, the concentration of nitrogen doping and bonding properties in the porous carbon can be well regulated, which is helpful to manipulate the crystal orientation of Pt nanoparticles and their dispersion and loading on the NPCs. Consequently, an improved oxygen reduction reaction (ORR) catalytic activity was successfully demonstrated in the optimized [email protected] composite with relatively lower content of Pt compared to the commercial catalyst Pt/C (20 wt%, JM). Moreover, the exceptional stability of the composite catalyst during ORR was experimentally verified by both the accelerated durability tests (ADT) and chronoamperometric i–t measurements. Intrinsically, pyridinic-N and graphitic-N were believed to be beneficial to the improved catalytic performance in the composite, while graphitic-N and pyridine-N-oxide were verified to be helpful to improve the stability as they can act as anchor of Pt NPs.

PdAu@MIL-100(Fe) cooperatively catalyze tandem reactions between amines and alcohols for efficient N-alkyl amines syntheses under visible light

PdAu@MIL-100(Fe), with PdAu alloy nanoparticles of ca. 1.7 nm encapsulated inside MIL-100(Fe) cavities, were prepared via a double-solvent impregnation followed by photoreduction. As compared with bare Pd@MIL-100(Fe), bimetallic PdAu@MIL-100(Fe) showed superior activities for the tandem reactions between amines and alcohols to produce N-alkyl amines under visible-light irradiation, ascribed to the promoting effect of metallic Au in the photocatalytic alcohol-to-aldehyde dehydrogenation. A Pd/Au ratio dependent N-alkylation activity was observed over PdAu@MIL-100(Fe), implying the possibility of synchronizing the reaction rates of two consecutive steps in the N-alkylation reaction, i.e., photocatalytic alcohol-to-aldehyde dehydrogenation and imines hydrogenation, to optimize the whole reaction. This study provides a highly efficient and stable catalytic system for the realization of alkylation of amines via a successful coupling of MOF-based photocatalysis and metal nanoparticle-based hydrogenation. This work also demonstrates that the reaction rates of different catalytic steps in a cascade/tandem reaction can be synchronized for an efficient overall reaction via a rational design of the multifunctional catalysts.

Pd catalyst supported on ZrO2‐Al2O3 by double‐solvent method for methane oxidation under lean conditions

AbstractThe Pd catalyst supported on the Zr0.5Al0.5O1.75 composite material was prepared by the conventional impregnation and double solvent impregnation method. The effects of preparation method on the catalytic properties of the Pd/Zr0.5Al0.5O1.75 catalyst for methane combustion have been investigated systematically. The measurement was evaluated in a multiple fixed‐bed continuous flow micro‐reactor by passing a gas mixture simulating the exhaust emissions from lean‐burn natural gas vehicles. The as‐prepared catalysts were characterized by CO chemical adsorption, transmission electron microscopy (TEM), hydrogen‐temperature programmed reduction (H2‐TPR),and X‐ray photoelectron spectroscopy (XPS) measurements. The results of TEM and CO chemisorption showed that the introduction of double solvent during the preparation of Pd/Zr0.5Al0.5O1.75 was beneficial for the dispersion of Pd nanoparticles and obtained superior resistance to the sintering of Pd on the surface of Zr0.5Al0.5O1.75. The H2‐TPR measurements demonstrated that the double solvent method increased the reducibility of the Pd catalyst. The XPS results further indicated that more active surface oxygen species also can be formed on the catalyst prepared via double solvent process. Thus, this catalyst exhibited better catalytic performance and hydrothermal aging resistance in the methane oxidation compared to its analogues with the same Pd content prepared by the conventional impregnation method.

Metal–organic framework immobilized cobalt oxide nanoparticles for efficient photocatalytic water oxidation

Water oxidation reactions driven by visible light play an important role in solar fuel production. Recently, catalysts based on earth abundant elements, such as cobalt oxides, have been studied extensively. Out of many factors, the catalyst particle size certainly affects the photocatalytic activity. To reduce the catalyst particle size below 5 nm without encountering agglomeration, a practical approach is to adopt a proper substrate to immobilize the catalyst nanoparticles. Herein, we utilized MIL-101, a highly porous and robust metal–organic framework (MOF), to immobilize cobalt oxide nanoparticles by a simple and facile method involving double solvent impregnation followed by a mild heat treatment. With cobalt loading in the range of 1.4–4.9 wt%, ultra small cobalt oxide nanoparticles (2–3 nm) have been successfully immobilized in the cages of MIL-101 with a good dispersion and narrow size distribution. Photocatalytic and electrochemical studies have indicated that the resultant cobalt oxide nanoparticles embedded in the MOF are highly efficient and stable water oxidation catalysts. A high turnover frequency (TOF) of 0.012 s−1 per cobalt atom and oxygen yield of 88% were obtained under the optimized conditions in the [Ru(bpy)3]2+–Na2S2O8 system. The MIL-101 support plays the roles of confining the size of catalyst nanoparticles and promoting charge transfer, leading to an enhanced photocatalytic performance.

Influence of Preparation Conditions on the Structure of MCM-41 and Catalytic Performance of Ru/MCM-41 in Benzene Hydrogenation

The influence of the preparation conditions on the structures of mesoporous molecular sieve MCM-41 were studied. The prepared MCM-41 samples were characterised by nitrogen physical adsorption–desorption, powder X-ray diffraction, transmission electron microscopy, FT-IR spectroscopy, thermo gravimetric analysis, differential scanning calorimetry and water/benzene static adsorption technologies. Ru/MCM-41 catalysts were then prepared by double solvent impregnation method and tested for benzene hydrogenation to cyclohexene. The structure characteristics of MCM-41 have a great effect on cyclohexene selectivity in benzene hydrogenation process. Ruthenium supported on MCM-41 with moderate surface area, larger pore size and pore volume, better long-range-order of hexagonal mesoporous shows better catalytic performance for benzene hydrogenation to cyclohexene.

Benzene hydrogenation over oxide-modified MCM-41 supported ruthenium–lanthanum catalyst: The influence of zirconia crystal form and surface hydrophilicity

The effects of the preparation conditions on the crystal form and surface properties of zirconia were studied. Mesoporous MCM-41 modified by tetragonal and monoclinic zirconia were synthesized by hydrothermal and precipitation methods. Then MCM-41 and zirconia-modified MCM-41 supported ruthenium–lanthanum catalysts were prepared via cyclohexane–water double solvent impregnation method. The obtained supports and catalysts were characterized by powder X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, N2 adsorption–desorption, thermogravimetric and differential scanning calorimetry, temperature programmed desorption of NH3, static water/benzene adsorption techniques. It has been found that MCM-41 modified by tetragonal zirconia with exclusive Lewis-acidic sites exhibits more surface hydroxyl groups and higher hydrophilicity than MCM-41 modified by monoclinic and amorphous zirconia. Tetragonal zirconia-modified MCM-41 supported ruthenium–lanthanum catalyst shows better catalytic performance in benzene hydrogenation to cyclohexene with benzene conversion of 54.4% and cyclohexene selectivity of 84.7%.

The Effect of Boron on Selective Benzene Hydrogenation to Cyclohexene over Ruthenium Boride Powders

The effects of the preparation conditions on the crystal form and surface properties of zirconia were studied. Mesoporous MCM-41 modified by tetragonal and monoclinic zirconia were synthesized by hydrothermal and precipitation methods. Then MCM-41 and zirconia-modified MCM-41 supported ruthenium–lanthanum catalysts were prepared via cyclohexane–water double solvent impregnation method. The obtained supports and catalysts were characterized by powder X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, N2 adsorption–desorption, thermogravimetric and differential scanning calorimetry, temperature programmed desorption of NH3, static water/benzene adsorption techniques. It has been found that MCM-41 modified by tetragonal zirconia with exclusive Lewis-acidic sites exhibits more surface hydroxyl groups and higher hydrophilicity than MCM-41 modified by monoclinic and amorphous zirconia. Tetragonal zirconia-modified MCM-41 supported ruthenium–lanthanum catalyst shows better catalytic performance in benzene hydrogenation to cyclohexene with benzene conversion of 54.4% and cyclohexene selectivity of 84.7%.

Dehydrogenation of methanol to methyl formate over CuSiO 2 catatysts prepared by ion exchange method

Stable and efficient Cu/SBA-15 and xCuZn/SBA-15 (x = 5, 10 and 15) in methanol dehydrogenation to methyl formate (MF) are prepared through a double-solvent impregnation (DI) method. Among all catalysts, 10CuZn/SBA-15 shows the highest catalytic performance with selectivity to MF about 88.1 % and methanol conversion of 31.1 %, which is attributed to the well-dispersed Cu particles and high ratio of Cu°/(Cu° + Cu+). The proper amount of ZnO could improve dispersion of Cu because of its geometrical spacer, inhibiting growth of Cu particle, and the best dispersion is achieved in 10CuZn/SBA-15. Furthermore, the Cu°/(Cu° + Cu+) ratio is greatly promoted with the assistance of ZnO, attributed to Cu-ZnO interaction, which reaches maxima of 53.3 % at a Cu/Zn mole ratio of 10. Specially, the optimized catalyst shows evident suitability at high temperature for methanol dehydrogenation reactions along with high level of conversion and selectivity for 100 h. Overall, our findings reveal that modification by the appropriate amount of ZnO in Cu-based catalyst has a positive impact on obtaining MF for the methanol dehydrogenation.