Dehua He

Multifunctional catalysis by Pd@MIL-101: one-step synthesis of methyl isobutyl ketone over palladium nanoparticles deposited on a metal–organic framework

Palladium nanoparticles deposited on a chromium terephthalate MIL-101 is a highly efficient multifunctional catalyst for the one-step synthesis of methyl isobutyl ketone, with significantly higher activity than palladium on traditional materials, such as metal oxides and zeolites.

Synthesis of isobutene from synthesis gas over nanosize zirconia catalysts

Abstract Performances of nanosize zirconium oxides prepared by precipitation, supercritical fluid drying (SCFD) and freeze-drying (FD) methods were evaluated for the selective synthesis of isobutene from synthesis gas (syn-gas). The crystal structure, particle size and specific surface area were measured by XRD, TEM and BET. The acidic and basic properties of the catalysts were studied by NH 3 - and CO 2 -TPD, respectively. The results showed that the crystal phases, acidic and basic properties of nanosize zirconia depend remarkably on the drying conditions. The catalysts over which the formation of isobutene is favored show a higher ratio of basic to acidic sites on their surfaces. The results of adding acidic and basic components into zirconia suggested that both the acidic and basic sites on the catalysts are required for the isosynthesis. The conversion of CO was increased by adding acidic component into zirconia, and the selectivity for i-C 4 H 8 was increased greatly by adding basic component into zirconia. It is suggested that the acidic sites are responsible for the activation of reactant molecules and the basic sites of the catalysts are significant for the formation of i-C 4 H 8 from CO hydrogenation.

Electrospun fibrous mats as skeletons to produce free-standing MOF membranes

Nanofibrous mats produced by electrospinning are ideal porous substrates for developing chemical systems due to their high specific surface area, large porosity, and enormous structural and chemical tunability. In this work, we report the fabrication of free-standing MOF membranes using electrospun nanofibrous mats as skeletons, and demonstrate the great potential of such nonwoven fiber mats as a new type of porous support in MOF research field. Direct deposition and seeded secondary growth approaches could be used to produce MOF materials within different nanofibrous skeletons, indicating that the developed method of generating MOF membranes has a remarkable flexibility. The characterizations performed show that the resulting products combine the unique properties of both electrospun nanofibers and MOFs, and can be regarded as a new class of hierarchically nanostructured functional materials.

Uncoordinated carbonyl groups of MOFs as anchoring sites for the preparation of highly active Pd nano-catalysts

A novel Tm-containing metal–organic framework, [Tm(μ2-L)(μ4-L)0.5(H2O)2]·3H2O (Tm-MOF), was prepared from the hydrothermal reaction of Tm(NO3)3 with 5-methylpyrazine-2-carboxylic acid in water. The 2,5-pyrazinedicarboxylate ligand (L) in Tm-MOF was formed in situ from 5-methylpyrazine-2-carboxylic acid under the above conditions. Tm-MOF is a three-dimensional (3D) coordination network with 1D open channels running across the coordination layers. Each L in bridging mode μ2 contains two uncoordinated carbonyl groups which point to the channels. By using the predesigned Tm-MOF as a host, we have successfully incorporated small palladium nanoparticles into the channels by a simple impregnation method. The Pd/Tm-MOF catalyst exhibited a high catalytic activity in the hydrogenation of styrene. Moreover, the catalyst could be reused at least three times without loss of any activity. In contrast, a low dispersion of metal and a low activity in styrene hydrogenation were observed over the Pd catalyst supported on ZIF-8, which has a similar surface area as the Tm-MOF, but no uncoordinated carbonyl groups. The results suggest that the uncoordinated carbonyl groups in the Tm-MOF may play an important role in facilitating the dispersion of Pd nanoparticles through an intermolecular interaction with the Pd cations in the course of immobilization.

Comparatively high yield methanol production from gas phase partial oxidation of methane

Gas phase partial oxidation of methane to methanol has been carried out in a specially designed reactor. A comparatively high yield of methanol (ca. 7–8%, methanol selectivity of 60% at methane conversion 13%) was obtained over a quite wide temperature range of more than 40 ◦ C at 5.0 MPa and CH4/O2/N2 = 100/10/10 (ml/min). The effects of the total flow rate, CH4/O2 ratio and pressure were examined and the superiority of the new reactor is discussed.

Condensation of formaldehyde and methyl formate to methyl glycolate and methyl methoxy acetate using heteropolyacids and their salts

Abstract Catalytic performances of heteropolyacids and their salts in the condensation of formaldehyde and methyl formate to methyl glycolate and methyl methoxy acetate have been studied. H 3 PW 12 O 40 and H 4 SiW 12 O 40 were found to have high activities for the formation of methyl glycolate and methyl methoxy acetate. The acidic salts of heteropolyacids also showed the activities in the condensation reactions, but the neutral salts of H 3 PW 12 O 40 and of H 4 SiW 12 O 40 were inactive. Thermal treatment of heteropolyacids was found to show a positive effect on the catalytic activities, and the most suitable pretreatment temperature was 300°C in the range 100–350°C. The investigating results of the influence of the reaction conditions showed that the molar ratios of formaldehyde to methyl formate and the reaction temperatures greatly affected the reaction. It was also found that the coexistence of water in the reaction system showed a negative effect on the catalytic activity.

A facile method for promoting activities of ordered mesoporous silica-anchored Rh–P complex catalysts in 1-octene hydroformylation

This work deals with the promotion of immobilized Rh catalyst activities in olefin hydroformylation by lengthening the alkyl spacers and choosing an active Rh precursor. The flexibility of long chain alkyls was used to free the motion of the anchored Rh complex in confining porous spaces so as to increase the substrate activation efficiency. RhCl(CO)(PPh3)2 was anchored to mesoporous silicas SBA-15 and MCM-41 through n-alkyl (carbon number n = 1, 3, 5, 8, 11) as spacer. The catalysts were characterized by X-ray powder diffraction (XRD), isothermal N2 sorption analysis and inductive coupling plasma-atomic emission spectroscopy (ICP-AES). The multi-step-assembly of the complex into surface-organic modified mesoporous silica was monitored and evidenced by infrared spectroscopy (IR). The prepared Rh-immobilized catalysts were applied in 1-octene hydroformylation to nonyl aldehydes. Rh leaching in the reaction solutions was determined by ICP-MS, which was found to be satisfyingly low along with successful catalyst cycles. With the increase of the alkyl spacer length, the specific activity (shown as turnover number, TON) and stability of the immobilized catalyst were both increased. The catalyst prepared by the longest alkyl spacer (n = 11, C11) revealed activity comparable to the homogeneous counterpart and resistance to the by-product poisoning. RhCl(CO)(PPh3)2-supported catalysts were also prepared by impregnating RhCl(CO)(PPh3)2 into SBA-15 and MCM-41 without the presence of diphenylphosphinoalkyl, the prepared catalysts showed a sharp activity decrease within only two catalyst cycles, owing to the significant active species leaching.

Direct partial oxidation of methane to methanol: Reaction zones and role of catalyst location

Abstract Direct partial oxidation of methane to methanol was investigated in a specially designed reactor. Methanol yield of about 7%–8% was obtained in gas phase partial oxidation. It was proposed that the reactor could be divided into three reaction zones, namely pre-reaction zone, fierce reaction zone, and post-reaction zone, when the temperature was high enough to initiate a reaction. The oxidation of methane proceeded and was completed mostly in the fierce reaction zone. When the reactant mixture entered the post-reaction zone, only a small amount of produced methanol would bring about secondary reactions, because molecular oxygen had been exhausted in the fierce reaction zone. A catalyst, if necessary, should be placed either in the pre-reaction zone, to initiate a partial oxidation reaction at a lower temperature, or in the fierce reaction zone to control the homogeneous free radical reaction.

Influence of acidic and basic properties of ZrO2 based catalysts on isosynthesis

Abstract Zirconium dioxide based catalysts were synthesized by mechanical mixing method and evaluated for the direct synthesis of isobutene and isobutane (i-C4) from CO hydrogenation. The experiments of temperature-programmed desorption of ammonia and carbon dioxide indicated that both the amount of acid–base sites and the strength of acid and base of the catalysts varied with the incorporation of promoters including various calcium salts, Al2O3 and KOH in ZrO2. The test results indicated that the activity and selectivity of the zirconia based catalysts depended on the acid–base properties of the catalysts. An appropriate amount of moderately strong acid–base sites and ratio of basic to acidic sites on the catalysts are significant for an active catalyst to selectively produce isobutene and isobutane from CO hydrogenation.

Glycerol hydrogenolysis to propanediols over supported Pd–Re catalysts

Supported Pd–Re bi-component catalysts were prepared by an impregnation method and employed in a glycerol hydrogenolysis reaction. The addition of Re into a Pd catalyst increased the conversion of glycerol and the selectivities to propanediols. The catalysts were characterized by N2 adsorption–desorption, XRD, CO chemisorption, TPR and NH3-TPD techniques. The results showed that the addition of Re changed the reduction behaviors of the Pd and Re components, indicating that Pd and Re might have an interaction. Re could increase the ability of the catalysts for the activation of a C–O bond and further promote the activity of Pd in glycerol hydrogenolysis. At the same time, the addition of Re also increased the acidity of the Pd–Re catalysts. Pd–Re supported on acidic oxides showed a tendency of decreasing selectivities to 1,2-propanediol, while Pd–Re catalysts with basic oxides as supports could increase the conversion of glycerol, but maintain the selectivities to 1,2-propanediol.