Accumulation Of Carbonate Deposits Research Articles

Influence of zinc oxide nanoparticles on the carbon accumulation on silver exposed to carbon dioxide hydrogenation reaction conditions.

The strong influence of surface adsorbates on the morphology of a catalyst is exemplified by studying a silver surface with and without deposited zinc oxide nanoparticles upon exposure to reaction gases used for carbon dioxide hydrogenation. Ambient pressure X-ray photoelectron spectroscopy and scanning tunneling microscopy measurements indicate accumulation of carbon deposits on the catalyst surface at 200 °C. While oxygen-free carbon species observed on pure silver show a strong interaction and decorate the atomic steps on the catalyst surface, this decoration is not observed for the oxygen-containing species observed on the silver surface with additional zinc oxide nanoparticles. Annealing the sample to temperatures above 350 °C removes the contaminants by hydrogenation to methane.

Kinetic Analysis of Dry Reforming of Methane on Traditional and Membrane Catalysts

The article presents an analysis of the results of a kinetic study of dry reforming of methane (UCM) in reactors with traditional (TC) and membrane catalysts (MC). The kinetic experiment in reactors with MC and TC was performed in the temperature range of 820–900°C and the ratio CH4 : CO2 = 1 : 1. In the experiment, an intensification of the process of the methane cracking reaction was established, the rate constant of which increases by an order of magnitude. Such a difference in the results of the DRM on the studied catalysts are due to the intensification of mass transfer on the MC, which is based on the phenomenon of thermal slip. A mathematical description corresponding to the kinetic scheme of DRM process is proposed, and the rates constants of direct and reverse reactions in both reactors are found. In the DRM process, water gas is formed on the TC, and synthesis gas is formed on the MC. At TC, the DRM process is accompanied by the accumulation of carbon deposits (CD), and at MC this accumulation is absent. The DRM process on both catalysts is characterized by three main reactions (methane cracking, gasification of the CD with carbon dioxide and/or water vapor and the reverse water gas shift), which were assumed to be reversible under experimental conditions. It turned out that on TC the gasification of the CD occurs in the reverse reaction of methane cracking, and on the MC—in the reactions of gasification by water vapor (mainly) and carbon dioxide. The process on the MC is characterized by irreversible reactions of methane cracking, gasification of the CD with water vapor and carbon dioxide. The reverse water gas shift reaction on the MC remains reversible, and its rate constants of the direct and inverse reactions turned out to be an order of magnitude lower than similar constants on the TC.

Изучение дезактивации цеолита H-ZSM-5 в процессе трансформации диметилового эфира в углеводороды в условиях in situ

Today, catalytic processes for the synthetic fuel components production are of considerable interest for both scientific and industrial area. The transformation of dimethyl ether into hydrocarbons is one of the possible solutions for the development of a closed hydrocarbon cycle, in connection with which a wide study of this process is an important task of modern catalysis. The transformation of dimethyl ether into hydrocarbons occurs with the formation of heavy polyaromatic hydrocarbons, which are deposited on the surface of active centers, which in turn prevents the further occurrence of chemical processes on their surface. This article presents a study of the deactivation of zeolite H-ZSM-5 by the thermogravimetric method in situ. The results of experiments carried out in the temperature range from to 300 to 400 °C are presented. The accumulation of carbon deposits in the first hour of operation indicates the presence of an induction period due to the formation of the first layer of carbon deposits. Linear decontamination occurs when the first five weight percent of carbon deposits accumulate. Further accumulation of carbon deposits up to eight weight percent leads to a sharp decrease in the rate of conversion of dimethyl ether into hydrocarbons to 0.08 kg (DME) / (kg (Cat) h). In the first hour of operation, aromatic hydrocarbons predominate in the reaction medium; with increasing time, the concentration of aromatic hydrocarbons decreases, and the concentration of light olefins and alkanes increases due to carbonization of the catalyst surface. The concentration of heavy aromatic hydrocarbons with a number of carbon atoms equal to or greater than eleven has a maximum after 240 minutes of reaction. The decrease in the content of heavy aromatic hydrocarbons after 240 minutes of reaction can be explained by the sharp loss of surface acidity due to carbonation.

The effects of Sn infiltration on dry reforming of biogas at solid oxide fuel cell operating conditions over Ni-YSZ catalysts

This work presents successful infiltration of Ni-YSZ-based catalysts for dry reforming of biogas over a temperature range of 600−800°C. Ni catalysts over YSZ support are commonly used as solid oxide fuel cell (SOFC) anode material to catalyse the fuel, normally hydrogen, in electrochemical oxidation reaction to generate electricity. The objective of this work is to find suitable SOFC anode catalyst materials to enable the SOFCs to operate on biogas as a renewable and low cost fuel. There are challenges when biogas is used as fuel; biogas dry reforming is slow and deleterious carbon deposition is unavoidable. The slow electrochemical reaction leads to low SOFC performance. While accumulation of carbon deposits may reduce the catalytic activity, decrease the SOFC performance and can lead to a complete failure of the SOFC operation. In this work, tin salt was used as a dopant in careful infiltration of Ni-YSZ catalysts. Characterisations of the catalysts were performed using SEM, XRF and XPS. Dry reforming reactions were carried out in a quartz tube reactor attached to a quadrupole mass spectrometer to monitor the product gases. Various compositions of CO2:CH4 mixtures were used to simulate biogas. It was observed that at small quantities of less than 1 weight % Sn/Ni loadings, dry reforming of biogas produced much higher level of the desired CO and H2 gas products compared to that obtained over non-infiltrated NiYSZ catalyst. The developed Sn-Ni-YSZ catalysts were able to operate continuously for more than 48 hours without noticeable performance degradation. More work is still in progress; however, this work so far concludes that Sn-doped Ni-YSZ catalysts have improved dry reforming of biogas at SOFC operating temperatures and so promised successful operations of SOFCs using biogas, a renewable fuel source, to produce sustainable electricity with high efficiency.

Two-dimensional modeling of the accumulation of carbonate deposits in marine environments

A program is developed for modeling the accumulation of deep-water, shallow-sea, reef and fragmentary carbonate deposits in marine environments. The formation of the Maldives carbonate platform is modeled using the developed program. The comparison of the modeling results and the geological cross-section demonstrates that the algorithms allow the construction of geological cross-sections in sufficient detail.

La0.6Sr0.4Co0.2Fe0.8O3 Perovskite: A Stable Anode Catalyst for Direct Methane Solid Oxide Fuel Cells

Direct methane solid oxide fuel cells, operated by supplying methane to a Ni/YSZ anode, suffer from degradation via accumulation of carbon deposits on the Ni surface. Coating a 40 µm thin film of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) perovskite on the Ni/YSZ anode surface decreased the amount of carbon deposits, slowing down the degradation rate. The improvement in anode durability could be related to the oxidation activity of LSCF which facilitates oxidation of CH4 and carbon deposits. Analysis of the crystalline structure of LSCF revealed that LSCF was stable in the reducing anode environment under H2 and CH4 flow at 750 °C and retained its perovskite structure throughout the 475 h long-term stability test.