Wenfeng Han

Direct Synthesis of Ruthenium‐Containing Ordered Mesoporous Carbon with Tunable Embedding Degrees by Using a Boric Acid‐Assisted Approach

Uniform ruthenium nanoparticles (1–2u2005nm) confined in ordered mesoporous carbon (Ru‐OMC) with various embedding degrees have been fabricated by using a boric acid‐assisted hard template method. The catalytic performance of Ru‐OMC catalysts was determined through the hydrogenation of toluene at 110u2009°C and 4.0u2005MPa. The effects of pore size and embedding degree on the catalytic performance were studied and compared with those of OMC‐supported ruthenium (Ru/OMC) catalysts with various pore sizes. The catalytic activities of embedding Ru‐OMC catalysts are much higher than those of supported Ru/OMC catalysts, which can be attributed to the strong interaction between ruthenium nanoparticles and the carbon support. Furthermore, the activities of Ru‐OMC catalysts are closely related to the embedding degree of ruthenium nanoparticles in the carbon matrix. The Ru‐OMC catalysts with an appropriate embedding degree affords a turnover frequency of up to 4.69u2005s−1 in toluene hydrogenation.

Preparation of fluorinated Cr2O3 hexagonal prism and catalytic performance for the dehydrofluorination of 1,1-difluoroethane to vinyl fluoride

A Cr2O3 hexagonal prism structure synthesized via the reaction of aqueous CrCl3 solution with NaBH4 solution at room temperature followed by calcination of the precipitate in N2 atmosphere at 500xa0°C is investigated as an efficient catalyst for dehydrofluorination of 1,1-difluoroethane producing vinyl fluoride. With the assistance of scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy, experimental results revealed that the uniform hexagonal prism has a prism length of 285xa0±xa043xa0nm and width of 233xa0±xa033xa0nm. It is in the form of loose and net-like aggregation of nano-Cr2O3 with diameter less than 3–5xa0nm with polycrystalline structure. NH3 temperature programmed desorption and chlorodifluoromethane dismutation experiments confirm the existence of relatively abundant and strong acidic sites. As a catalyst for dehydrofluorination of 1,1-difluoroethane, compared with commercial Cr2O3, much higher activity and stability were observed due to the evolution of CrOxFy species and much higher surface area and mesoporous structure. No significant morphology changes or sintering of the catalyst are observed after 70-h reaction. Compared with the commercial Cr2O3, we suggest that the much smaller size of Cr2O3 crystalline which possesses higher surface energy, lower strength, and more abundant Lewis acidity and the formation of CrOxFy during reaction over hexagonal prism catalyst probably contributes to the activity and stability difference between these two catalysts.Graphical Abstract

Activation of a Carbon Support Through a Two‐Step Wet Oxidation and Highly Active Ruthenium–Activated Carbon Catalysts for the Hydrogenation of Benzene

A two‐step liquid oxidation approach was developed for the activation of carbon materials. Following nitric acid treatment and subsequent liquid oxidation by a mild oxidant such as H2O2, the number of surface acidic functional groups was increased without destroying the physical structures of the carbon materials. Ruthenium catalysts supported on activated carbon prepared by this two‐step liquid oxidation method show significantly improved Ru dispersion and excellent catalytic performance in the hydrogenation of benzene. The dispersion of ruthenium and the catalytic performance of Ru/activated carbon increases monotonically with the amount of surface functional groups.

Geometric effect of Ru/HSAG@mSiO2: a catalyst for selective hydrogenation of cinnamaldehyde

A new strategy to synthesize a catalyst consisting of graphite-supported Ru nanoparticles encapsulated by mesoporous silica layers was developed via a facile and scalable wet-chemical process. The intended structures were confirmed with N2 sorption, CO chemisorption, TEM and SEM. The geometric effect of the pores in the silica layer of Ru/HSAG@mSiO2 was evaluated in the hydrogenation of cinnamaldehyde and showed 15% higher selectivity to unsaturated alcohol and three times higher turnover frequency (TOF) relative to unconfined Ru/HSAG catalyst with the equivalent size of Ru particles.

Effect of pore structure of mesoporous carbon on its supported Ru catalysts for ammonia synthesis

Mesoporous carbon (MC) was prepared by a hard-template method and used as support for the preparation of a Ru-based ammonia synthesis catalyst, Ba-Ru-K/MC. N2 adsorption-desorption, scanning electron microscopy, and transmission electron microscopy were used to characterize the mesoporous carbon and its supported Ru catalysts. The effects of pore structure of the Ba-Ru-K/MC catalyst on its performance for ammonia synthesis were studied. The results show that the surface area of the mesoporous carbon material varies with the SiO2/C mass ratio and reaches the largest at 1.0 of SiO2/C. The catalytic activity of Ba-Ru-K/MC for ammonia synthesis increases with increased mesoporous surface area of the mesoporous carbon. The reaction rate of ammonia synthesis is 139 mmol/(gcat·h) at 425 °C, 10 MPa, and a gas hourly space velocity of 10000 h−1.

Effect of the graphitic degree of carbon supports on the catalytic performance of ammonia synthesis over Ba-Ru-K/HSGC catalyst

A series of high surface area graphitic carbon materials (HSGCs) were prepared by ball-milling method. Effect of the graphitic degree of HSGCs on the catalytic performance of Ba-Ru-K/HSGC-x (x is the ball-milling time in hour) catalysts was studied using ammonia synthesis as a probe reaction. The graphitic degree and pore structure of HSGC-x supports could be successfully tuned via the variation of ball-milling time. Ru nanoparticles of different Ba-Ru-K/HSGC-x catalysts are homogeneously distributed on the supports with the particle sizes ranging from 1.6 to 2.0 nm. The graphitic degree of the support is closely related to its facile electron transfer capability and so plays an important role in improving the intrinsic catalytic performance of Ba-Ru-K/HSGC-x catalyst.

Solution combustion synthesis of nano-chromia as catalyst for the dehydrofluorination of 1,1-difluoroethane

Nano-Cr2O3 was prepared via solution combustion synthesis (SCS) with Cr(NO3)3·9H2O as the Cr precursor and glycine as the fuel. The effect of molar ratio of glycine to Cr in the feed during solution combustion was investigated. Cr2O3 samples were characterized by XRD, SEM, TEM, H2-TPR, and XPS. In addition, these catalysts were evaluated for the dehydrofluorination of 1,1-difluoroethane producing vinyl fluoride (VF, CH2=CHF). The results confirm that Cr2O3 is in relatively uniform flakes or flat particles via solution combustion synthesis with the particle size of 50–200xa0nm and composed by the aggregation of 58–77xa0nm nanoparticles. The specific surface area of higher than 30xa0m2xa0g−1 is achieved, which is comparable to the values obtained by solvothermal route. For the dehydrofluorination of 1,1-difluoroethane, high conversion levels (83xa0% for commercial catalyst and 93xa0% for SCS catalyst) are achieved at 350xa0°C, and the activity of SCS catalyst is at least 2× higher than that of commercial Cr2O3 at reaction temperatures below 300xa0°C. Compared with commercial Cr2O3, XPS, and H2-TPR reveal the higher CrO3 contents on the surface of Cr2O3 derived from SCS. It is suggested that CrO3 plays a major role in the catalytic performance as high-valent Cr species such as Cr(VI) are vital for the reaction because they could be transformed to the active species such as CrOxFy. In addition to the high activity, compared with commercial Cr2O3, SCS catalyst also show higher stability. Following the reaction of 120xa0h at 300xa0°C, no noticeable deactivation is observed while the activity of commercial Cr2O3 declines with TOS. High surface area and much smaller size of Cr2O3 crystalline favors the formation of CrOxFy during reaction over Cr2O3-3.33 catalyst probably contribute to the high activity and stability.

Preparation of efficient ruthenium catalysts for ammonia synthesis via high surface area graphite dispersion

AbstractnHigh surface area graphite (HSAG) was tested as a support of ruthenium catalyst for ammonia synthesis. As it is in the form of fine powder, it can be dispersed in the ruthenium precursor solution achieving high dispersion of Ru and efficiency. The surface area, porosity, crystalline structure of support, morphology, dispersion of Ru, desorption of H2 and N2 and methanation of the catalyst were investigated by N2 physisorption, XRD, SEM, TEM and TPD/TPSR techniques. The results show that higher ammonia synthesis rates of the HASG catalyst compared to activated carbon can be achieved with the assistance of ultrasonic treatment. As expected, the methanation rate over HSAG is much lower than that of activated carbon over the whole temperature range studied.

Sub-nano MgF2 embedded in carbon nanofibers and electrospun MgF2 nanofibers by one-step electrospinning as highly efficient catalysts for 1,1,1-trifluoroethane dehydrofluorination

Hydrofluorocarbons (HFCs) which are usually potent greenhouse gases are regulated by the Montreal Protocol and its amendments, especially the recent Kigali Amendment. Dehydrofluorination of HFCs is an efficient route for the conversion of these greenhouse gases to value added and environmentally benign chemicals. Although AlF3 with strong Lewis acidity catalyzes dehydrofluorination, it also favors carbon deposition. MgF2 with weak acidity inhibits coking significantly. Unfortunately, MgF2 sinters dramatically at temperatures below 300 °C leading to the low activity for dehydrofluorination. In the present work, we report that sub-nano MgF2 embedded in carbon fibers and electrospun MgF2 fibers prevent sintering of MgF2 during dehydrofluorination reaction. Via simple and one-step electrospinning and calcination in a N2 (for embedded MgF2) or air (for MgF2 fibers) atmosphere, embedded MgF2 with particle sizes between 3–6 nm and pure MgF2 fibers with diameters of around 100 nm were fabricated. No sintering was observed following reaction at 450 °C. The fine MgF2 particles and MgF2 fibers facilitate the formation of under coordinated Mg species in MgF2 which are the weak acid sites. By embedding MgF2 or fabrication of MgF2 fibers, weak acid sites are increased significantly, while strong acid sites remain almost unchanged. Hence, they show significantly higher reaction rates than MgF2 prepared by precipitation of Mg(CH3COO)2·4H2O with NH4F for the dehydrofluorination of 1,1,1-trifluoroethane (HFC-143a) to VDF (CH2CF2) at 450 °C.

Data for: Morphological effect of fluorinated alumina on the Cl/F exchange reaction

reaction Wenfeng Han a, b, , Shenglan Zhou ,Miao Xi a , Haili Wang , Wucan Liu b, , Haodong Tang, Zhikun Wang , Chunpeng Zhang a a Institute of Catalysis, Zhejiang University of Technology, Hangzhou 310014, Zhejiang, PR China b Zhejiang Research Institute of Chemical Industry, Hangzhou 310023, Zhejiang, PR China c State Key Laboratory of Fluorinated Greenhouse Gases Replacement and Control Treatment, Hangzhou 310023, Zhejiang, PR China E-mail: jackhanwf@hotmail.com; hanwf@zjut.edu.cn (W.F. Han) tanghd@zjut.edu.cn (H.D. Tang)