Guiru Wang

A Facile Approach to Fabricate an N‐Doped Mesoporous Graphene/Nanodiamond Hybrid Nanocomposite with Synergistically Enhanced Catalysis

Owing to their unique structural features and surface properties, graphene and nanodiamond have attracted tremendous attention in diverse fields. However, restacking of graphene and reagglomeration of dispersed nanodiamond inevitably depress their catalytic properties. Herein, inspired by the historic discovery of “pillared clay”, we successfully realized the simultaneous inhibition of their restacking by fabricating a N‐doped mesoporous graphene/nanodiamond (N‐RGO/ND) nanocomposite by a facile wet‐chemical approach. The electrocatalytic oxygen reduction reaction (ORR) and the thermocatalytic oxidant‐free and steam‐free direct dehydrogenation (DDH) of ethylbenzene were used to examine its catalytic properties. The nanocomposite showed synergistically improved catalytic DDH and electrocatalytic ORR activity relative to that of the individual components, which can be ascribed to synergy between graphene and nanodiamond and to the large surface area, well‐ordered mesoporous structure, small crystalline size, and rich defect and CO surface features. Moreover, the developed synthetic strategy in this work can be extended to diverse N‐doped nanocomposites from dispersion‐required carbon precursors.

Guanidine Nitrate Enhanced Catalysis of Nitrogen‐Doped Carbon Nanotubes for Metal‐Free Styrene Production through Direct Dehydrogenation

Nitrogen‐doped carbon nanotubes (CNTs) with defect‐ and CO‐group‐rich surface features were fabricated through a facile and scalable physical dry milling and subsequent pyrolysis approach of carbon nanotubes and melamine in the presence of guanidine nitrate. The catalytic performance of the as‐prepared N‐doped CNTs with diverse guanidine nitrate dosages and pyrolysis temperatures for direct dehydrogenation of ethylbenzene to styrene under oxidant‐ and steam‐free conditions was measured. Various characterization techniques including high‐resolution transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, nitrogen–adsorption and thermogravimetric analysis, and Raman spectroscopy were employed to investigate the structure and surface properties, as well as to explore the relationship between catalyst nature and catalytic performance. It is found that the addition of guanidine nitrate in the pyrolysis process of CNT with melamine significantly affects the structure, surface properties, and catalytic performance. The optimized N‐doped CNTs demonstrate steady‐state styrene production rates 1.56 and 1.60 times higher than those of the parent CNTs and the established nanodiamond, as well as 6.49 times the rate of commercially available K–Fe catalyst without compromising the selectivity to styrene. The much superior catalytic performance in metal‐free catalytic direct dehydrogenation can be ascribed to the CO group‐ and defect‐rich surface nature, the basic properties resulted from N‐doping, the larger surface area and pore volume, and smaller graphitic carbon crystallites. The fabricated novel N‐doped CNTs can be considered as a promising candidate for sustainable production of styrene through oxidant‐ and steam‐free direct dehydrogenation of ethylbenzene with energy‐saving and environmentally benign features. The developed defect‐formation strategy in this work can be used for preparation of other metal‐free carbocatalysts.

Facile simultaneous defect production and O,N-doping of carbon nanotubes with unexpected catalytic performance for clean and energy-saving production of styrene

O,N-doped carbon nanotubes with increased structural defects and enriched surface ketonic CO groups (MN-CNT), prepared by a facile and low-cost one-step strategy, demonstrate unexpected catalytic performance in direct dehydrogenation of ethylbenzene for styrene production with clean and energy-saving features. This work paves a new avenue for preparing other highly-efficient carbocatalysts in diverse organic transformations.

Explosive decomposition of a melamine-cyanuric acid supramolecular assembly for fabricating defect-rich nitrogen-doped carbon nanotubes with significantly promoted catalysis.

A facile and scalable approach for fabricating structural defect-rich nitrogen-doped carbon nanotubes (MCSA-CNTs) through explosive decomposition of melamine-cyanuric acid supramolecular assembly is presented. In comparison to pristine carbon nanotubes, MCSA-CNT exhibits significantly enhanced catalytic performance in oxidant- and steam-free direct dehydrogenation of ethylbenzene, demonstrating the potential for metal-free clean and energy-saving styrene production. This finding also opens a new horizon for preparing highly-efficient carbocatalysts rich in structural defect sites for diverse transformations.

Increased active sites and their accessibility of a N-doped carbon nanotube carbocatalyst with remarkably enhanced catalytic performance in direct dehydrogenation of ethylbenzene

This work presents an efficient and low-cost one-step strategy for simultaneously N-doping and increasing surface ketonic CO groups and structural defects of a N-doped carbon nanotube (HN-CNT) through the explosive decomposition of hexamethylenetetramine (HTA) nitrate, a low-cost N,O-containing organic compound. The as-synthesized HN-CNT demonstrates a 1.64 and 2.19 times higher steady-state styrene rate with 98.5% selectivity towards styrene for direct dehydrogenation (DDH) than that of the parent CNT and H-CNT prepared by the similar pyrolysis procedure to that for the HN-CNT except for replacing HTA nitrate with HTA.

Methane formation route in the conversion of methanol to hydrocarbons

Abstract The influence factors and paths of methane formation during methanol to hydrocarbons (MTH) reaction were studied experimentally and thermodynamically. The fixed-bed reaction results show that the formation of methane was favored by not only high temperature, but also high feed velocity, low pressure, as well as weak acid sites dominated on deactivated catalyst. The thermodynamic analysis results indicate that methane would be formed via the decomposition reactions of methanol and DME, and the hydrogenolysis reactions of methanol and DME. The decomposition reactions are thermal chemistry processes and easily occurred at high temperature. However, they are influenced by catalyst and reaction conditions through DME intermediate. By contrast, the hydrogenolysis reactions belong to catalytic processes. Parallel experiments suggest that, in real MTH reactions, the hydrogenolysis reactions should be mainly enabled by surface active H atom which might come from hydrogen transfer reactions such as aromatization. But H 2 will be involved if the catalyst has active components like NiO.

Facile, low-cost, and scalable fabrication of particle size and pore structure tuneable monodisperse mesoporous silica nanospheres as supports for advanced solid acid catalysts

Monodisperse mesoporous silica nanospheres (MSN) have been emerging as one of the new frontiers in materials science and nanotechnology because of their potential medical and biological applications as well as heterogeneous catalysis. Although the synthesis of MSN with various morphologies and sphere size has been reported, the synthesis of MSN with monodisperse control below 200 nm by a facile, scalable and low-cost method with high tetraethylorthosilicate (TEOS) concentration still remains a challenge. Herein, this goal was achieved by a templating hydrothermal technique using cetyltrimethylammonium bromide (CTAB) as the templating surfactant and low-cost urea as mineralizing agent. The mesoporous feature and diameter of nanosphere of MSN can be efficiently adjusted. The high volume efficiency by using high TEOS concentration as Si sources and the low production cost by using urea as mineralizing agent for synthesizing MSN allow this novel technique to have great potential for industrial production. Furthermore, the advanced solid acid catalysts with superior catalytic activity and stability were prepared by supporting phosphotungstic acid (PTA) on MSN, ascribed to the high PTA dispersity and facilitated mass transfer by the short mesoporous channels in comparison with traditional mesoporous silica like MCM-41. This work presents an alternative method for overcoming low stability issue, a bottleneck problem for the industrial application of solid acid catalysts.

Modulating the microstructure and surface chemistry of carbocatalysts for oxidative and direct dehydrogenation: A review

Abstract The catalytic performance of solid catalysts depends on the properties of the catalytically active sites and their accessibility to reactants, which are significantly affected by the microstructure (morphology, shape, size, texture, and surface structure) and surface chemistry (elemental components and chemical states). The development of facile and efficient methods for tailoring the microstructure and surface chemistry is a hot topic in catalysis. This contribution reviews the state of the art in modulating the microstructure and surface chemistry of carbocatalysts by both bottom-up and top-down strategies and their use in the oxidative dehydrogenation (ODH) and direct dehydrogenation (DDH) of hydrocarbons including light alkanes and ethylbenzene to their corresponding olefins, important building blocks and chemicals like oxygenates. A concept of microstructure and surface chemistry tuning of the carbocatalyst for optimized catalytic performance and also for the fundamental understanding of the structure-performance relationship is discussed. We also highlight the importance and challenges in modulating the microstructure and surface chemistry of carbocatalysts in ODH and DDH reactions of hydrocarbons for the highly-efficient, energy-saving, and clean production of their corresponding olefins.

Morphology effect of zirconia support on the catalytic performance of supported Ni catalysts for dry reforming of methane

Abstract An immature pinecone shaped hierarchically structured zirconia (ZrO 2 -ipch) and a cobblestone-like zirconia nanoparticulate (ZrO 2 -cs), both with the monoclinic phase (m-phase), were synthesized by the facile hydrothermal method and used as the support for a Ni catalyst for the dry reforming of methane (DRM) with CO 2 . ZrO 2 -ipch is a much better support than ZrO 2 -cs and the traditional ZrO 2 irregular particles made by a simple precipitation method (ZrO 2 -ip). The supported Ni catalyst on ZrO 2 -ipch (Ni/ZrO 2 -ipch) exhibited outstanding catalytic activity and coke-resistant stability compared to the ones on ZrO 2 -cs (Ni/ZrO 2 -cs) and ZrO 2 -ip (Ni/ZrO 2 -ip). Ni/ZrO 2 -ip exhibited the worst catalytic performance. The origin of the significantly enhanced catalytic performance was revealed by characterization including XRD, N 2 adsorption measurement (BET), TEM, H 2 -TPR, CO chemisorption, CO 2 -TPD, XPS and TGA. The superior catalytic activity of Ni/ZrO 2 -ipch to Ni/ZrO 2 -cs or Ni/ZrO 2 -ip was ascribed to a higher Ni dispersion, increased reducibility, enhanced oxygen mobility, and more basic sites with a higher strength, which were due to the unique hierarchically structural morphology of the ZrO 2 -ipch support. Ni/ZrO 2 -ipch exhibited better stability for the DRM reaction than Ni/ZrO 2 -ip, which was ascribed to its higher resistance to Ni sintering due to a strengthened metal-support interaction and the confinement effect of the mesopores and coke deposition resistance. The higher coking resistance of Ni/ZrO 2 -ipch for the DRM reaction in comparison with Ni/ZrO 2 -ip orignated from the coke-removalability of the higher amount of lattice oxygen and more basic sites, confirmed by XPS and CO 2 -TPD analysis, and the stabilized Ni on the Ni/ZrO 2 -ipch catalyst by the confinement effect of the mesopores of the hierarchical ZrO 2 -ipch support. The superior catalytic performance and coking resistance of the Ni/ZrO 2 -ipch catalyst makes it a promising candidate for synthesis gas production from the DRM reaction.

Tuning of the textural features and acidic properties of sulfated mesoporous lanthana-zirconia solid acid catalysts for alkenylation of diverse aromatics to their corresponding α-arylstyrenes

The textural features and acidic properties of sulfated mesoporous lanthana-zirconia solid acids (SO 4 2- /meso-La 0.1 Zr 0.9 O δ ) were efficiently tuned by modifying the conditions used to prepare the meso-La 0.1 Zr 0.9 O δ composites, such as the molar ratio of the template to La and Zr metal ions ( N t/m ), molar ratio of ammonia to La and Zr metal ions ( N a/m ), hydrothermal temperature ( T hydro ), and hydrothermal time ( t hydro ). The effect of the textural features and acidic properties on the catalytic performance of solid acid catalysts for alkenylation of p -xylene with phenylacetylene was investigated. Various characterization techniques such as N 2 physisorption, X-ray diffraction, NH 3 temperature-programmed desorption, and thermogravimetric analysis were employed to reveal the relationship between the nature of catalyst and its catalytic performance. It was found that the catalytic performance significantly depended on the textural features and acidic properties, which were strongly affected by preparation conditions of the meso-La 0.1 Zr 0.9 O δ composite. Appropriate acidic sites and high accessibility were required to obtain satisfactory catalytic reactions for this reaction. It was also found that the average crystallite size of t -ZrO 2 affected by the preparation conditions had significant influence on the ultrastrong acidic sites of the catalysts. The optimized SO 4 2- /meso-La 0.1 Zr 0.9 O δ catalyst exhibited much superior catalytic activity and coke-resistant stability. Moreover, the developed SO 4 2- /meso-La 0.1 Zr 0.9 O δ catalyst demonstrated excellent catalytic performance for alkenylation of diverse aromatics with phenylacetylene to their corresponding α-arylstyrenes. Combining the previously established complete regeneration of used catalysts by a facile calcination process with the improved catalytic properties, the developed SO 4 2- /meso-La 0.1 Zr 0.9 O δ solid acid could be a potential catalyst for industrial production of α-arylstyrenes through clean and atom efficient solid-acid-mediated Friedel-Crafts alkenylation of diverse aromatics with phenylacetylene.