Yitao Dai

Nitrogen-doped nanotubes-decorated activated carbon-based hybrid nanoarchitecture as a superior catalyst for direct dehydrogenation

A novel N-doped activated carbon (AC) based nanostructure decorated with nanotubes (N-CNT-AC) has been successfully fabricated through a facile and scalable approach involving the mechanical milling and subsequent solid pyrolysis of the low-cost and commercially available AC and melamine. Various characterization techniques including high resolution transmission electron microscopy, X-ray diffraction, nitrogen adsorption, X-ray photoelectron spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy were employed to reveal the relationship between catalyst features and catalytic performance in the oxidant- and steam-free direct dehydrogenation (DDH) of ethylbenzene to styrene. Although the as-synthesized AC-based hybrid nanostructure has a much lower surface area (397.0 cm2 g−1) and pore volume (0.17 cm3 g−1) than the parent AC (777.1 cm2 g−1 surface area and 0.4 cm3 g−1 pore volume), it demonstrates 1.74 and 3.67 times the steady-state styrene rate of the per gram parent AC and the industrially-used K–Fe catalyst, respectively, for the DDH reaction, which is ascribed to the promoting effect of the unique hybrid microstructure, the surface rich CO group and defect/edge feature, the increased basic properties through N-introduction into the hybrid nanostructure, the small size of the graphitic crystallite, as well as the inherent high surface and large porosity of the AC-based materials. The in situ Fourier transform infrared spectroscopy measurement suggests a lower activation energy over the developed novel N-doped AC-based hybrid nanostructure for the DDH reaction than over the parent AC. Interestingly, the developed hybrid nanocomposite exhibits a much superior selectivity for styrene production compared to the parent AC, which is ascribed to the N-doping into the AC-based matrix. The developed N-doped AC-based hybrid nanostructure catalyst could be a potential candidate for catalytic styrene production via steam- and oxidant-free direct dehydrogenation of ethylbenzene.

Improvement of nano-particulate CexZr1−xO2 composite oxides supported cobalt oxide catalysts for CO preferential oxidation in H2-rich gases

The Co3O4/CexZr1−xO2 is a potential catalyst for CO preferential oxidation (CO PROX) in excess hydrogen. This study is devoted to the optimization of the nano-particulate CeO2–ZrO2 supported cobalt oxide catalysts. The effects of Ce/(Ce + Zr) atomic ratio, Co3O4 loading, calcination temperature, as well as reaction conditions like addition of CO2 and H2O, gas hourly space velocity (GHSV) and O2 concentration on the catalytic properties were investigated. Moreover, the temperature programmed reduction (TPR) and the powder X-ray diffraction (XRD) techniques were used to reveal the relationship between catalyst nature and catalytic properties. Results demonstrate that the catalytic performance of Co3O4/CexZr1−xO2 catalysts is strongly dependent on the H2 uptake, reduction temperature and crystallite size affected by Ce/(Ce + Zr) atomic ratio, cobalt oxide loading and calcination temperature. It is also found that the developed catalyst possesses high catalytic stability, and no obvious decrease in either CO conversion or CO2 selectivity can be observed even with the existence of CO2 and H2O in the feed. 16 wt.%Co3O4/Ce0.85Zr0.15O2 calcined at 450 °C could be a promising catalyst for the CO PROX reaction to eliminate trace CO from H2-rich gas.

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.

Mesostructured Co–Ce–Zr–Mn–O composite as a potential catalyst for efficient removal of carbon monoxide from hydrogen-rich stream

Mesostructured CoxCe0.85Zr0.15MnyOe composites were firstly prepared by a simple one-pot surfactant-assisted co-precipitation (SACP) method and then employed to catalyze the CO preferential oxidation (CO PROX) reaction in an H2-rich stream. Effects of the Co and Mn contents (x and y, respectively) in the formula, as well as the presence of H2O and CO2 in feed were investigated. The as-synthesized Co0.4Ce0.85Zr0.15Mn0.10Oe catalyst showed excellent catalytic performance in the CO PROX reaction: 100% CO conversion could be observed in a wide temperature range of 140–200 °C; even in the simulated syngas, the almost complete CO removal could still be achieved at 175–225 °C; no obvious change in both CO conversion and CO2 selectivity over the catalyst took place during the CO PROX process with simulated syngas as feed. N2 physisorption (BET), temperature-programmed reduction (TPR), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopic (XPS) characterization techniques were employed to reveal the relationship between the catalyst nature and catalytic performance. The outstanding catalytic performance in CO PROX reaction was remarkably dependent on a larger specific surface area, more reducible Co3+ and the high dispersity of the Co3O4, affected by the Co and Mn contents through strong Co–Ce–Zr–Mn interactions. The mesostructured Co0.4Ce0.85Zr0.15Mn0.10Oe catalyst prepared by the simple one-pot SACP protocol can be a promising candidate for CO PROX reaction in excess H2.

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.