chemical-precipitation-method-for-synthesis-nb2o5-modified-bulk

Chemical Precipitation Method for the Synthesis of Nb<sub>2</sub>O<sub>5</sub> Modified Bulk Nickel Catalysts with High Specific Surface Area

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of ...

tuning-acidity-pt-cnts-catalysts-for-hydrodeoxygenation-diphenyl

Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid ...

Dalian University of Technology

Carbon nanofiber-supported Co nanocomposites were prepared by means of a modified ethylene glycol (EG) process, in which the Co salts are reduced in EG and are subsequently deposited onto carbon nanofibers (CNFs). It has been found that the deposition of cobalt colloids onto CNFs can be tailored by simply adjusting the pH of the EG and by heating the mixture of CNFs and colloidal solution at 100 degrees C for some time. The pH value (<7) and the temperature (at least 100 degrees C) for heating the mixture of CNFs and colloidal solution are found to be the key factors for depositing Co particles onto CNFs. The obtained Co/CNFs have a high and homogeneous dispersion of spherical Co metal particles with a narrow size distribution of 10-15 nm with a peak around 13.5 nm; this result is consistent, to a certain degree, with the value of 12.8 nm obtained from the XRD study. The different states of the stabilizer including carboxylates (pH>7) and carboxylic acids (pH<7) as well as the decomposition of carboxylic acids during heat treatment were monitored by using FTIR and UV-visible spectroscopy. On the basis of experimental results, the mechanism of depositing cobalt colloids onto CNFs is also addressed. The as-synthesized Co/CNF catalysts show excellent activity and regioselectivity for the 1-octene hydroformylation.

Co/CNF catalysts tailored by controlling the deposition of metal colloids onto CNFs: preparation and catalytic properties.

Carbon nanotubes fabricated by the dc arc discharge method (ADCNTs) and chemical vapor deposition method (CVDCNTs) were oxidized with concentrated HNO 3 to modify their surface chemistry. The materials were characterized using SEM, TEM, FTIR, XPS, potentiometric titration, and nitrogen adsorption. The initial and oxidized materials were used as adsorbents of cadmium from aqueous solutions with different pH. Langmuir and Freundlich adsorption models were applied to fit the isotherm data, and both models fit the experimental data very well. The acid oxidation resulted in an increase in the number of oxygen-containing groups without drastic changes in the texture of the adsorbents. Although the small volume of micropores is present, the nanotube structure can be considered as nonporous. The lack of developed microporosity in carbonaceous materials eliminates the inner surface diffusion problems and makes the vast majority of surface groups available for adsorption of cadmium. The availability of these centers depends on the pH of the solution, which controls the protonation level. In spite of the fact that the pH of the solution affects the speciation of cadmium to some degree, the surface chemistry is the predominant force for adsorption at the pH range adopted in the present study, while the texture of materials also affects the nanotube's cadmium-adsorbing performance.

Investigation of the role of surface chemistry and accessibility of cadmium adsorption sites on open-surface carbonaceous materials.

CoSi particles on a silica support, synthesized by metal organic chemical vapor deposition (MOCVD) of Co(SiCl(3))(CO)(4) as a precursor at atmospheric pressure and moderate temperature in a fluidized bed reactor, show high catalytic activity and selectivity in naphthalene hydrogenation.

CoSi particles on silica support as a highly active and selective catalyst for naphthalene hydrogenation.

Silica supported CoSi particles were synthesized by metal organic chemical vapor deposition of the Co(SiCl(3))(CO)(4) precursor carried in hydrogen at atmospheric pressure and moderate temperature in a fluidized bed reactor. In contrast, CoCl(2) supported on silica was formed by using argon as the carrier gas. The samples were characterized by X-ray diffraction, transmission electron microscopy, ultraviolet-visible spectroscopy, and thermogravimetric/differential thermogravimetric analysis. The precursor Co(SiCl(3))(CO)(4) reacted with the hydroxyl groups of amorphous silica via loss of HCl and introduced cobalt species onto the surface. The decomposition mechanism of the supported precursor on silica was investigated by in situ Fourier transform infrared spectroscopy from room temperature to 300 °C in a hydrogen or argon atmosphere. The results showed that CO and HCl elimination occurred in a hydrogen atmosphere, while only CO elimination occurred in Ar. All of the results showed that it was possible to prepare supported CoSi at lower temperatures via changing the carrier gas.

The formation mechanism of cobalt silicide on silica from Co(SiCl3)(CO)4 by in situ Fourier transform infrared spectroscopy.

Effective utilization of coal bed methane is very significant for energy utilization and environment protection. Catalytic combustion of methane is a promising way to eliminate trace amounts of oxygen in the coal bed methane and the key to this technology is the development of high-efficiency catalysts. Herein, we report a series of CeLaO(x = 0-0.8) monolithic catalysts for the catalytic combustion of methane, which are prepared by citric acid method. The structural characterization shows that the substitution of La enhance the oxygen vacancy concentration and reducibility of the supports and promote the migration of the surface oxygen, as a result improve the catalytic activity of CeO. M-CeLaO(monolithic catalyst, CeLaOcoated on cordierite honeycomb) exhibits outstanding activity for methane combustion, and the temperature for 10 and 90% methane conversion are 495 and 580 °C, respectively. Additionally, CeLaOmonolithic catalyst presents excellent stability at high temperature. These CeLaOmonolithic materials with a small amount of La incorporation therefore show promises as highly efficient solid solution catalysts for lean-oxygen methane combustion. Graphical abstract ᅟ.

Enhanced activity and stability of La-doped CeOmonolithic catalysts for lean-oxygen methane combustion.

Bimetallic Co-Re/TiO catalysts were developed for efficient citral hydrogenation. Bimetallic catalysts were prepared by co-impregnation (CI), successive-impregnation (SI), and surface redox method (SR). The arrangement between the Co and Re species on these systems was fully characterized using several techniques (TEM-energy-dispersive X-ray spectroscopy, H temperature-programmed reduction, temperature-programmed desorption, XRD, CO FTIR spectroscopy, model reaction of cyclohexane dehydrogenation), and their catalytic performances were evaluated for the selective hydrogenation of citral towards unsaturated alcohols. The Re and Co species are completely isolated in the CI sample, presenting a very limited Co-Re interaction. In SI samples, the metals coexist in a Janus-type structure with a concentration of Re around Co. Decoration/core-shell structures are observed for SR samples resulting from the redox exchange between the metallic surface of the parent Co/TiO catalyst and the Re species of the modifier precursor salt. The contact degree between the two metals gradually increases as follows: Isolated structure (CI)<Janus-type structure(SI)<decoration/core-shell structure (SR). The unchanging structure of all SI samples independent of the Re loading leads to similar electron transfer, and the increase in Re content results in agglomeration of Re, thus decreasing the catalytic activity. Density-of-state (DOS) calculations prove that the high valence of Re is a disadvantage for the hydrogenation reaction. For SR samples, the increase of Re loading contributes to the electron transfer from Re to Co that is consistent with a change of structure from decoration to core-shell. The lack of directly accessible Co atoms for SR catalysts with fully coated structure decreases the efficiency of Re reduction. The presence of Co-Re interaction resulting from the close contact between metals plays a dominant role in the hydrogenation of citral. Nevertheless, an excessively high contact degree is unnecessary for citral hydrogenation once Co-Re interaction has formed.

Supported Co-Re Bimetallic Catalysts with Different Structures as Efficient Catalysts for Hydrogenation of Citral.

With the help of DFT calculations, the reaction mechanisms of the rhodium(III)-catalyzed C-H activation/annulation between aromatic amide and α-allenol leading to the formation of isoindolinone have been theoretically investigated. Our calculated results show that the catalytic cycle consists of four stages: N-H deprotonation and C-H activation (Stage I), allene insertion, rearrangement and isomerization (Stage II), β-H elimination and enol-keto tautomerism (Stage III), and catalyst regeneration resulting in the five-membered ring product (Stage IV). For stage IV, besides the reaction paths proposed by the experimentalists, i.e., the insertion and reductive elimination (labeled as path a) and the reductive elimination and hydroamination (labeled as path b), an alternative path which involves C-N and C-H reductive eliminations (labeled as path c) was proposed and examined. The computational results show that the newly established path c is more energetically favorable than the reaction paths proposed by the experimentalists (paths a and b). The allene (non-terminal double bond) insertion step contributes to the rate-determining step with an overall activation free energy of 24.6 kcal/mol. Our study is beneficial for a better comprehension of the reaction mechanisms and provides a significant suggestion for further development of similar reactions.

Mechanism of Rhodium(III)-Catalyzed C-H Activation/Annulation of Aromatic Amide with α-Allenol: A Computational Study.

The fabrication of bimetallic catalysts has been taken great focus in the concept of heterogeneous catalysis due to their high efficiency and economic concerns. In this work, a series of bimetallic Ru-Re catalysts were designed and synthesized for the selective hydrogenation of dimethyl terephthalate (DMT) to 1,4-cyclohexane dicarboxylate (DMCD) under mild condition. Characterization techniques including the XRD, TEM, STEM-HAADF EDX elemental mapping, H2-TPR, and XPS were used to study the surface chemical property, the morphology, as well as the catalytic behavior of different samples. It was revealed that the monometallic Ru catalyst already has the capacity to activate and transform DMT into DMCD. Whilst the promotion effect can be optimized to a maximum with only small amount of Re, with the mass ratio of Ru/Re as 10:1. It was also revealed that the addition of Re could largely enhance the distribution of surface active metal species, facilitate the charge transfer between Ru and Re, as well as strengthen the Ru-Re synergistic interaction, which further led to the modification of the redox ability and the catalytic performances of samples. However, excessive addition of Re caused strong interaction between Ru and Re, and further limited the H₂ activation and the seasonable release of the active reducible metal species, which was responsible for the depressed catalytic performances in the presence of higher Re loading. The RuRe/AC catalyst displayed the DMT conversion of 82% with DMCD selectivity of 96% under mild condition of 70 °C at 3 MPa. The specific rate of RuRe/AC based on per gram of Ru was 0.44 mol·g Ru·h.

Selective Hydrogenation of Dimethyl Terephthalate to 1,4-Cyclohexane Dicarboxylate by Highly Dispersed Bimetallic Ru-Re/AC Catalysts.

Designing a highly active, stable and cost-effective electrocatalyst with multiple functionalities toward hydrogen evolution and oxygen reduction applications is crucial for the development of renewable energy sources. Here, the synthesis of hollow PtNi nanostrings via a facile two-step template method is reported. The PtNi nanostrings own Pt-rich rough surfaces, and hollow string-like structure with the structural disorder morphology. Impressively, the unique hollow PtNi nanostrings exhibit excellent electrocatalytic activity toward the hydrogen evolution and oxygen reduction reactions. The obtained overpotential is only 44.60 mV at current density of 10 mA cm for hydrogen evolution reaction. Furthermore, the hollow PtNi nanostrings exhibit a high mass activity of 2.5 A mg and a superior specific activity of 3.89 mA cm at 0.90 V versus reversible hydrogen electrode in oxygen reduction reaction, respectively, which are 10 and 9 times higher than those of the commercial Pt/C. This work provides a promising approach for the synthesis of highly bifunctional electrocatalysts with a hollow sting-like structure to promote their application in the hydrogen evolution and oxygen reduction reactions.

ArticleTotal : 2	Year
Publication title	2018
Publication title	2019

Article	Year
Co/CNF catalysts tailored by controlling the deposition of metal colloids onto CNFs: preparation and catalytic properties. Chemistry (Weinheim an der Bergstrasse, Germany)\| PubMed ID: 16389617	2006
Investigation of the role of surface chemistry and accessibility of cadmium adsorption sites on open-surface carbonaceous materials. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 18817419	2008
CoSi particles on silica support as a highly active and selective catalyst for naphthalene hydrogenation. Chemical communications (Cambridge, England)\| PubMed ID: 19333486	2009
The formation mechanism of cobalt silicide on silica from Co(SiCl3)(CO)4 by in situ Fourier transform infrared spectroscopy. Physical chemistry chemical physics : PCCP\| PubMed ID: 21483930	2011
Enhanced activity and stability of La-doped CeOmonolithic catalysts for lean-oxygen methane combustion. Environmental science and pollution research international\| PubMed ID: 29222662	2017
Supported Co-Re Bimetallic Catalysts with Different Structures as Efficient Catalysts for Hydrogenation of Citral. ChemSusChem\| PubMed ID: 30620120	2019
Mechanism of Rhodium(III)-Catalyzed C-H Activation/Annulation of Aromatic Amide with α-Allenol: A Computational Study. The Journal of organic chemistry\| PubMed ID: 30735381	2019
Selective Hydrogenation of Dimethyl Terephthalate to 1,4-Cyclohexane Dicarboxylate by Highly Dispersed Bimetallic Ru-Re/AC Catalysts. Journal of nanoscience and nanotechnology\| PubMed ID: 31383114	2020
Template-Preparation of Hollow PtNi Nanostrings as a Bifunctional Electrocatalyst for the Hydrogen Evolution and Oxygen Reduction Reactions. Journal of nanoscience and nanotechnology\| PubMed ID: 31383121	2020

Changhai Liang

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