Haodong Tang

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

Uniform ruthenium nanoparticles (1–2 nm) 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 110 °C and 4.0 MPa. 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 4.69 s−1 in toluene hydrogenation.

Improved catalytic performance of encapsulated Ru nanowires for aqueous-phase Fischer–Tropsch synthesis

Fischer–Tropsch (F–T) synthesis at low temperature has attracted a lot of research attention due to its thermodynamically favorable nature at low temperature. Herein, we report a highly efficient solid nanoreactor for low temperature liquid-phase F–T synthesis. The solid nanoreactor was fabricated by encapsulation of Ru–PVP nanowires in ethane–silica hollow nanospheres via a one-pot co-condensation method. Under similar reaction conditions, the solid nanoreactor shows higher activity (activity: 6.35 versus 5.96 molCO mol−1Ru h−1) and selectivity towards oxygenate products (41.3 versus 21.6%) than free Ru–PVP in aqueous F–T synthesis. The high activity and selectivity of the encapsulated Ru–PVP is mainly attributed to the low PVP/Ru ratio and the unique yolk–shell nanostructure in increasing the degree of exposure of the active sites. It was also observed that the selectivity towards C5–12 products could be increased to 63.8% in a water/cyclohexane biphasic system. Encapsulation not only gave rise to the quasi-homogeneous Ru–PVP with facile recycling ability, but also enhanced its activity and selectivity towards oxygenates.

Solid state synthesis of Ru–MC with highly dispersed semi-embedded ruthenium nanoparticles in a porous carbon framework for benzoic acid hydrogenation

A mesoporous ruthenium containing carbon Ru–MC-g catalyst with a semi-embedded uniform Ru particle distribution was synthesized by using a dry grinding method using nano-silica as a hard template. The structure and catalytic performance of the embedded Ru–MC-g catalysts were compared with those of the Ru–MC-i catalyst prepared via a wet impregnation method and the carbon supported Ru catalyst (Ru/MC). Among all the obtained catalysts, the Ru–MC-g catalyst prepared by the dry-grinding process shows excellent hydrogenation catalytic activity performance for the chemoselective hydrogenation of benzoic acid to cyclohexane carboxylic acid. The turnover frequency of the Ru–MC catalyst reaches ca. 2400 h−1 at 4 MPa, 120 °C, which is a 6 times improvement compared with that of supported Ru/MC catalyst. The dry-grinding process is expected to be easily scaled up for large-scale production of Ru-based catalysts.

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 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.

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

Abstract High 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.

Pyrolysis of trifluoromethane over activated carbon: role of the surface oxygen groups

The pyrolysis of CHF3 and CHClF2 over activated carbons was investigated at 823 K, GHSV of 1820 h–1 and pressure of 1 bar. To elucidate the mechanism, activated carbons were treated in H2 at 1123 K, HNO3 solution at 363 K, N2 at 873 K or supported with 4 wt% poly(acrylic acid sodium salt), respectively. The results confirm that following different treatments, the concentration of surface oxygen groups on activated carbons varies dramatically. These surface groups play important roles in the decomposition of CHF3 and the product profiles. It is suggested that carboxylic groups are responsible for the formation of CF3 and ultimately the product C2F6 which results from the coupling of CF3, while the interaction between CHF3 and hydroxyl or lactonic groups leads to the total destruction of CHF3 and production of CO and CO2. Pyrolysis of CHClF2 over activated carbon confirms that surface oxygen groups have no noticeable influence on the reactions of CF2. By contrast, a pure carbon surface is responsible for the disproportionation of CF2 and formation of CF3.

Easy synthesis of iron doped ordered mesoporous carbon with tunable pore sizes

Abstract Precise control of the pore sizes for porous carbon materials is of importance to study the confinement effect of metal particles because the pore size in nanosize range will decide the physical and chemical properties of the metal nanoparticles. In this paper, we report a new approach for the synthesis of iron doped ordered mesoporous carbon materials with adjustable pore size using Fe-SBA-15 as hard template and boric acid as the pore expanding reagent. The pore size can be precisely adjusted by a step of 0.4 nm in the range of 3–6 nm. The carbonization temperature can be lowered to 773 K due to the catalytic role of the doped iron. The present approach is suitable for facile synthesis of metal imbedded porous carbon materials with tunable pore sizes.

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.