Papers by Keyword: Reaction Mechanism

Abstract: Understanding the process of water oxidation, especially intermediate species, represents an important step toward gaining a mechanistic understanding of new emerging catalysts. The aim of this study is exploring the process of water oxidation and electrolyte orientation under external potential when using an emerging water oxidation catalyst, CoB_i, in sodium borate (NaBi) buffer using in situ attenuated–total-reflection Fourier transform infrared spectroscopy (ATR-FTIR) spectroscopy. CoB_i is generated via electrodeposition from aqueous solutions containing borate and Co²⁺. IR spectra were obtained for CoB_i films under applied potentials supporting water oxidation catalysis. The spectra of water and CoB_i on ZnSe/Cr/Au electrode surfaces change in intensity and their slope depends on the potential, which is rarely reported. The appearance of new bands at certain potentials is interpreted in terms of the potential-dependent re-alignment of water and borate molecules both from the film and electrolyte. A superoxide surface intermediate at 1027 cm^-1 was observed in both thin and thick films. It is proposed to be Co (III)OO*H bridging and relates to a fast water oxidation process. The chemical structure of the intermediate species is proposed finally.

Abstract: Octahedral layered birnessite (OL) was synthesized by redox method, and OL supported Ag catalysts (xAg/OL, x = 0.1wt%, 0.2wt%, 0.3wt%, 0.5wt%) were prepared by ion exchange method. Then catalysts were characterized by XRD, SEM, BET, H₂-TPR, TG, O₂-TPD and in-situ DRIFTS, while the catalytic activity of CO was evaluated. Among xAg/OL samples, the 0.3Ag/OL exhibited the best catalytic activity for CO oxidation (T₅₀ = 105 ^oC and T₉₀ = 135 ^oC). The results show that the chemical adsorption of oxygen, the low-temperature reducibility and the strong interaction between the Ag species and OL are related to the excellent catalytic activity of xAg/OL. The reaction mechanism was studied by in-situ DRIFTS. First, O₂ was adsorbed and activated on the oxygen vacancies of xAg/OL, then formed oxygen free radical attacked the adsorbed CO and produced CO₂, subsequently CO₂ desorbed from the catalyst surface. Oxygen vacancies was supplemented by gas O₂, thus circulating.

Abstract: The paper studied the thermal mechanical shearing of waste tire rubber (WTR) by tetra methyl thiuram disulfide (TMTD), a reclaiming agent. The results showed that the mooney viscosity, gel content and crosslink density of the WTR decreased with the increasing TMTD amount. The mechanical properties of recycled rubber were best in the amount of 1% TMTD, which could reach 14MPa and 368%, respectively. The molecular weight of WTR was analyzed by gel permeation chromatorgraphy (GPC). The molecular weight of rubber dropped more faster when the content of TMTD from 0.5% to 1%. The plausible reaction mechanism of TMTD on the process of cross-linking degradation was predicted based on the changes of the mooney viscosity, gel content, crosslink density and the relation between the molecular weight and the Raman spectroscopy of the sol fraction.

Abstract: The pozzolanic additions are widely used as concrete component for numerous technical, economic and environmental reasons. Obviously the hydration process in a pozzolana containing system differs from hydration of Ordinary Portland Cement (OPC) what is indicated macroscopically by slower increase of strength and lower hydration heat. This paper aims to study pozzolanic reaction from perspective of chemical kinetics. From this point of view pozzolanic reaction and carbonation are two parallel reactions which are competing for portlandite (Ca (OH)₂). The rate of each of these two reactions is characterized by rate constant and order of reaction. The system under study was 1:1 mixture lime – ceramic powder. The course of reaction was primarily studied by thermogravimetry which results were further subjected to kinetic analysis. MAS NMR spectroscopy was used for study of structural changes taking place in material in the course of pozzolanic reaction.

Abstract: The reduction kinetics of ilmenite was investigated. Phase evolution during the reduction process was identified by XRD and morphology change was observed using SEM. Kinetic parameters of the activation energy and pre-exponential factor were determined by Kissinger-Akahira-Sunose (KAS) method and Coast-Redfern method&artificial isokinetic relationship (IKP) respectively. Results showed that when the reaction of titanium suboxides makes a growing contribution, the conversion dependence of activation energy has an ascending trend. When the conversion exceeded 0.7, the reactants almost consumed, and the process was controlled by diffusion.

Abstract: This paper has proved that best material ratio is n (KAlSi₃O₈) : n (CaSO₄) : n (C) = 2:7:3 in carbon-thermal reduction of potash feldspar and phosphogypsum for preparation potassium sulfate, which is based on thermodynamic calculation and analysis, combined with experimental study. XRD analysis shows that generated solid content is K₂SO₄, CaSiO₃ and Ca₂Al₂SiO₇ at the batching system. Under the above ingredients system, the production ways of potassium sulfate have three possible. It depends on operating temperature of the system. At the same time, the phosphogypsum reduction conditions and decomposition rate is controlling factor that potassium sulfate is generated in the system.

Abstract: In this paper, the reaction mechanism of inorganic carbon and titanium dioxide synthesis of titanium carbide thermodynamic were explored, and a thermodynamic basis date for the microwave heating was provided. Through analyzing the experimental results for the thermal stability of titanium carbide, we could obtain the theoretical parameters for the actual synthesis process.

Abstract: According to XRD, DTA and SEM detections, the hydration products of blast furnace slag based cementing material SL, SLG. were studied in different age periods. The XRD analysis of cementing material SL hydration products showed the composition of hydration products were mainly amorphous substances, few crystalline substances. Characteristic peak of ettringite, such as AFt, hadn’t been found in the spectral line of DTA, and it hadn’t been found in the figures of SEM, either, which was accordant with the conclusion that the cementing performance of SL mainly coming from gel of hydrated calcium silicate (CSH) and hydrated calcium aluminate. But the cementing performance of SLG mainly coming from Aft, CSH and AFm from hydration products analysis of different age periods.

Abstract: In proton exchange membrane (PEM) fuel cell cathode, oxygen reduction reaction (ORR) behavior have important effects on fuel cell performance. In this paper, the dynamic oxygen adsorption model and then the redox reaction model for hydrogen and oxygen system were established on the surface of the electricity catalyst Pt. The reaction process of hydrogen and oxygen on the surface of Pt was simulated by first-principles molecular dynamics method, and the influence of temperature on oxygen reduction reaction characteristics was analyzed. The simulation results show that the oxygen atom adsorption on the Pt (111) surface and reaction with the first hydrogen atom are the control step of the oxygen reduction reaction; and the oxygen reduction reaction accelerates with increasing temperature, but the temperature does not affect the geometric structure of the products in the oxygen reduction reaction steps. The results of the simulation agree well with our previous first-principles calclation, and this will be helpful for understanding the mechanism of oxygen reduction reaction in PEM fuel cell cathode.

Abstract: Sr₃Ti₂O₇ ceramics with pure Ruddlesden-Popper phase (RP) were synthesized by conventional solid state method. The influences of the Bi₂O₃ addition, the calcination temperature, and the sintering temperature on the phase transition were studied. The results showed that for the samples without doping Bi₂O₃, the main phase of calcined powders is Sr₃Ti₂O₇, but pure Sr₃Ti₂O₇ phase cannot be obtained in the sintered ceramics because of the Sr₃Ti₂O₇ decomposition. For the samples doping with Bi₂O₃, although the main phase of the calcined powder is SrTiO₃, the single RP phase Sr₃Ti₂O₇ can be obtained after sintering, which should be attributed to the formation of Sr₃Bi₂O₆ phase during calcination stage. Bi₂O₃ addition is beneficial to the formation of the Sr₃Ti₂O₇ RP phase.