scholarly journals Understanding Surface Basic Sites of Catalysts: Kinetics and Mechanism of Dehydrochlorination of 1,2-Dichloroethane over N-Doped Carbon Catalysts

Catalysts ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 707 ◽  
Author(s):  
Zhaobing Shen ◽  
Yejun Han ◽  
Yue Liu ◽  
Yejun Qin ◽  
Ping Xing ◽  
...  
Keyword(s):  
Vinyl Chloride ◽  
Active Sites ◽  
Reaction Rate ◽  
Surface Reaction ◽  
Catalytic Performance ◽  
High Energy ◽  
Carbon Catalyst ◽  
Base Strength ◽  
Carbon Catalysts ◽  
Pyridinic N

The production of vinyl chloride (VCM) by pyrolysis of 1,2-dichloroethane (DCE) is an important process in the ethylene-based poly(vinyl chloride) industry. The pyrolysis is performed at temperatures above 500 °C, gives low conversions, and has high energy consumption. We have shown that N-doped carbon catalysts give excellent performances in DCE dehydrochlorination at 280 °C. The current understanding of the active sites, mechanism, and kinetics of DCE dehydrochlorination over N-doped carbon catalysts is limited. Here, we showed that pyridinic-N on a N-doped carbon catalyst is the active site for catalytic production of vinyl chloride monomer from DCE. The results of CO2 and DCE temperature-programmed desorption experiments showed that the pyridinic-N catalytic sites are basic, and the mechanism of dehydrochlorination on a N-doped carbon catalyst involves a carbanion. A kinetic study of dehydrochlorination showed that the surface reaction rate on the N-doped carbon catalyst was the limiting step in the catalytic dehydrochlorination of DCE. This result enabled clarification of the dehydrochlorination mechanism and optimization of the reaction process. These findings will stimulate further studies to increase our understanding of the relationship between the base strength and catalytic performance. The results of this study provide a method for catalyst optimization, namely modification of the amount of pyridinic-N and the base strength of the catalyst, to increase the surface reaction rate of DCE dehydrochlorination on N-doped carbon catalysts.

scholarly journals Principle understanding towards synthesizing Fe/N decorated carbon catalysts with pyridinic-N enriched and agglomeration-free features for lithium–oxygen batteries

RSC Advances ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 3853-3860 ◽  
Author(s):  
Gangning Zhang ◽  
Li Zhang ◽  
Shangqian Zhao ◽  
Shigang Lu ◽  
Yan Lu ◽  
...  
Keyword(s):  
Carbon Catalyst ◽  
Carbon Catalysts ◽  
Lithium Oxygen Batteries ◽  
Pyridinic N

Synthesizing a pyridinic-N enriched and agglomeration-free Fe/N-decorated carbon catalyst for lithium–oxygen batteries.

Low temperature modified sludge-derived carbon catalysts for efficient catalytic wet peroxide oxidation of m-cresol

2017 ◽  
Vol 19 (5) ◽  
pp. 1362-1370 ◽  
Author(s):  
Yamin Wang ◽  
Huangzhao Wei ◽  
Ying Zhao ◽  
Wenjing Sun ◽  
Chenglin Sun
Keyword(s):  
Low Temperature ◽  
Catalytic Performance ◽  
Peroxide Oxidation ◽  
Carbon Catalyst ◽  
Wet Peroxide Oxidation ◽  
Catalytic Wet Peroxide Oxidation ◽  
Carbon Catalysts ◽  
Excellent Catalytic Performance

A sludge-derived carbon catalyst modified at 0 °C revealed excellent catalytic performance in the CWPO reaction of m-cresol.

scholarly journals Waste-Derived Green Nanocatalyst for Biodiesel Production: Kinetic-Mechanism Deduction and Optimization Studies

2021 ◽  
Vol 13 (11) ◽  
pp. 5849
Author(s):  
Chee Yoong Chooi ◽  
Jia Huey Sim ◽  
Shiau Foon Tee ◽  
Zhi Hua Lee
Keyword(s):  
Active Sites ◽  
Reaction Rate ◽  
Surface Reaction ◽  
Pore Diameter ◽  
Preparation Method ◽  
Kinetic Mechanism ◽  
Transesterification Reaction ◽  
Biodiesel Production ◽  
Rate Limiting Step ◽  
Rate Limiting

This research focuses on deducing the kinetic mechanism for biodiesel production catalyzed by a CaO nanocatalyst derived from waste cockle shells via thermal hydration–dehydration treatment. In addition, the CaO nanocatalyst preparation method via thermal hydration–dehydration-related parameters (hydration duration, recalcination temperature, and recalcination duration) was studied and optimized. The transesterification reaction catalyzed by the CaO nanocatalyst followed the Langmuir–Hinshelwood kinetic mechanism with surface reaction as the rate-limiting step. The relatively low activation energy (3786.7 J/mol) for a transesterification reaction offered by the CaO nanocatalyst enhanced the reaction rate to 27.3% FAME yield/hr. The optimal conditions for the thermal hydration–dehydration treatment used to develop the nano CaO catalyst were 6 h of hydration duration, 650 °C of recalcination temperature, and 3 h of recalcination duration. Of biodiesel yield, 94.13% was obtained at a moderate temperature of 60 °C and 3 h reaction time during the transesterification of palm oil catalyzed by the nano-CaO. SEM, BET, and TPD results proved that the CaO nanocatalyst had a large surface area (13.9113 m2/g) and high pore volume (0.0318 cm3/g) that were rich in active sites (1046.46 μmol CO2/g), and the pore diameter (33.17 nm) was accessible to reactants and products.

The design and catalytic performance of molybdenum active sites on an MCM-41 framework for the aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran

2019 ◽  
Vol 9 (3) ◽  
pp. 811-821 ◽  
Author(s):  
Zhao-Meng Wang ◽  
Li-Juan Liu ◽  
Bo Xiang ◽  
Yue Wang ◽  
Ya-Jing Lyu ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Active Sites ◽  
Aerobic Oxidation ◽  
Catalytic Performance ◽  
Mcm 41

The catalytic activity decreases as –(SiO)3Mo(OH)(O) > –(SiO)2Mo(O)2 > –(O)4–MoO.

Catalytic Resonance Theory: Parallel Reaction Pathway Control

2019 ◽  
Author(s):  
M. Alexander Ardagh ◽  
Manish Shetty ◽  
Anatoliy Kuznetsov ◽  
Qi Zhang ◽  
Phillip Christopher ◽  
...  
Keyword(s):  
Chemical Reactions ◽  
Active Site ◽  
Active Sites ◽  
Reaction Pathway ◽  
Control Strategies ◽  
Oscillation Amplitude ◽  
Catalytic Performance ◽  
Parallel Reaction ◽  
Resonance Theory ◽  
Static Conditions

Catalytic enhancement of chemical reactions via heterogeneous materials occurs through stabilization of transition states at designed active sites, but dramatically greater rate acceleration on that same active site is achieved when the surface intermediates oscillate in binding energy. The applied oscillation amplitude and frequency can accelerate reactions orders of magnitude above the catalytic rates of static systems, provided the active site dynamics are tuned to the natural frequencies of the surface chemistry. In this work, differences in the characteristics of parallel reactions are exploited via selective application of active site dynamics (0 < ΔU < 1.0 eV amplitude, 10<sup>-6</sup> < f < 10<sup>4</sup> Hz frequency) to control the extent of competing reactions occurring on the shared catalytic surface. Simulation of multiple parallel reaction systems with broad range of variation in chemical parameters revealed that parallel chemistries are highly tunable in selectivity between either pure product, even when specific products are not selectively produced under static conditions. Two mechanisms leading to dynamic selectivity control were identified: (i) surface thermodynamic control of one product species under strong binding conditions, or (ii) catalytic resonance of the kinetics of one reaction over the other. These dynamic parallel pathway control strategies applied to a host of chemical conditions indicate significant potential for improving the catalytic performance of many important industrial chemical reactions beyond their existing static performance.

Structural/Texture Evolution During Facile Substitution of Ni into ZSM-5 Nanostructure vs. its Impregnation Dispersion Used in Selective Transformation of Methanol to Ethylene and Propylene

2020 ◽  
Vol 23 ◽  
Author(s):  
Parisa Sadeghpour ◽  
Mohammad Haghighi ◽  
Mehrdad Esmaeili
Keyword(s):  
High Temperature ◽  
Physicochemical Properties ◽  
Active Sites ◽  
Catalytic Performance ◽  
Fixed Bed Reactor ◽  
Light Olefins ◽  
Isomorphous Substitution ◽  
Impregnation Method ◽  
Hydrothermal Temperature ◽  
X Ray

Aim and Objective: Effect of two different modification methods for introducing Ni into ZSM-5 framework was investigated under high temperature synthesis conditions. The nickel successfully introduced into the MFI structures at different crystallization conditions to enhance the physicochemical properties and catalytic performance. Materials and Methods: A series of impregnated Ni/ZSM-5 and isomorphous substituted NiZSM-5 nanostructure catalysts were prepared hydrothermally at different high temperatures and within short times. X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray (EDX), Brunner, Emmett and Teller-Barrett, Joyner and Halenda (BET-BJH), Fourier transform infrared (FTIR) and Temperature-programmed desorption of ammonia (TPDNH3) were applied to investigate the physicochemical properties. Results: Although all the catalysts showed pure silica MFI–type nanosheets and coffin-like morphology, using the isomorphous substitution for Ni incorporation into the ZSM-5 framework led to the formation of materials with lower crystallinity, higher pore volume and stronger acidity compared to using impregnation method. Moreover, it was found that raising the hydrothermal temperature increased the crystallinity and enhanced more uniform incorporation of Ni atoms in the crystalline structure of catalysts. TPD-NH3 analysis demonstrated that high crystallization temperature and short crystallization time of NiZSM-5(350-0.5) resulted in fewer weak acid sites and medium acid strength. The MTO catalytic performance was tested in a fixed bed reactor at 460ºC and GHSV=10500 cm3 /gcat.h. A slightly different reaction pathway was proposed for the production of light olefins over impregnated Ni/ZSM-5 catalysts based on the role of NiO species. The enhanced methanol conversion for isomorphous substituted NiZSM-5 catalysts could be related to the most accessible active sites located inside the pores. Conclusion: The impregnated Ni/ZSM-5 catalyst prepared at low hydrothermal temperature showed the best catalytic performance, while the isomorphous substituted NiZSM-5 prepared at high temperature was found to be the active molecular sieve regarding the stability performance.

Efficient Production of Biodiesel Catalyzed by Acidic Nanoporous Carbon Materials：A Review

2020 ◽  
Vol 16 ◽  
Author(s):  
Anping Wang ◽  
Heng Zhang ◽  
Hu Li ◽  
Song Yang
Keyword(s):  
Pore Structure ◽  
Active Sites ◽  
Catalytic Performance ◽  
Nanoporous Carbon ◽  
Biodiesel Production ◽  
Efficient Production ◽  
Fossil Energy ◽  
Catalytic Materials ◽  
High Acid ◽  
Carbon Based

Background: With the gradual decrease of fossil energy, the development of alternatives to fossil energy has attracted more and more attention. Biodiesel is considered to be the most potent alternative to fossil energy, mainly due to its green, renewable and biodegradable advantages. The stable, efficient and reusable catalysts are undoubtedly the most critical in the preparation of biodiesel. Among them, nanoporous carbon-based acidic materials are very important biodiesel catalysts. Objective: The latest advances of acidic nanoporous carbon catalysts in biodiesel production was reviewed. Methods: Biodiesel is mainly synthesized by esterification and transesterification. Due to the important role of nanoporous carbon-based acidic materials in the catalytic preparation of biodiesel, we focused on the synthesis, physical and chemical properties, catalytic performance and reusability. Results: Acidic catalytic materials have a good catalytic performance for high acid value feedstocks. However, the preparation of biodiesel with acid catalyst requires relatively strict reaction conditions. The application of nanoporous acidic carbon-based materials, due to the support of carbon-based framework, makes the catalyst have good stability and unique pore structure, accelerates the reaction mass transfer speed and accelerates the reaction. Conclusion: Nanoporous carbon-based acidic catalysts have the advantages of suitable pore structure, high active sites, and high stability. In order to make these catalytic processes more efficient, environmentally friendly and low cost, it is an important research direction for the future biodiesel catalysts to develop new catalytic materials with high specific surface area, suitable pore size, high acid density, and excellent performance.

scholarly journals Efficient Catalytic Conversion of Polysulfides by Biomimetic Design of “Branch-Leaf” Electrode for High-Energy Sodium–Sulfur Batteries

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Wenyan Du ◽  
Kangqi Shen ◽  
Yuruo Qi ◽  
Wei Gao ◽  
Mengli Tao ◽  
...  
Keyword(s):  
Active Sites ◽  
High Performance ◽  
Electrochemical Reaction ◽  
Molecular Layer ◽  
Specific Capacity ◽  
High Energy ◽  
Reduction Reaction ◽  
Biomimetic Design ◽  
Co Nanoparticles ◽  
Sodium Sulfur

AbstractRechargeable room temperature sodium–sulfur (RT Na–S) batteries are seriously limited by low sulfur utilization and sluggish electrochemical reaction activity of polysulfide intermediates. Herein, a 3D “branch-leaf” biomimetic design proposed for high performance Na–S batteries, where the leaves constructed from Co nanoparticles on carbon nanofibers (CNF) are fully to expose the active sites of Co. The CNF network acts as conductive “branches” to ensure adequate electron and electrolyte supply for the Co leaves. As an effective electrocatalytic battery system, the 3D “branch-leaf” conductive network with abundant active sites and voids can effectively trap polysulfides and provide plentiful electron/ions pathways for electrochemical reaction. DFT calculation reveals that the Co nanoparticles can induce the formation of a unique Co–S–Na molecular layer on the Co surface, which can enable a fast reduction reaction of the polysulfides. Therefore, the prepared “branch-leaf” CNF-L@Co/S electrode exhibits a high initial specific capacity of 1201 mAh g−1 at 0.1 C and superior rate performance.

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