CO Disproportionation Reaction Research Articles

Investigation of limiting H2O/CO2 co-electrolysis to convert renewable electricity into chemical energy using solid oxide electrolysis cell

H2O/CO2 co-electrolysis offers an efficient way to convert renewable electricity into chemical energy. However, carbon deposition is a serious problem for H2O/CO2 co-electrolysis. In this work, limiting electrolytic potential, limiting electrolytic voltage and conversion ratios of H2O/CO2 co-electrolysis are investigated. At low temperatures, the limiting potential of H2O/CO2 co-electrolysis is low and the conversion ratio cannot reach high because solid carbon is easily formed through CO electrolysis or disproportionation reactions. At high temperatures, the electrolytic voltage and conversion ratios of H2O and CO2 can reach high because CO electrolysis or disproportionation reactions are not easy to take place. The conversion ratios of CO2 and H2O can reach 99.6 % and 99.4 % at the H2O/CO2 ratio of 1:1 and 1273 K without solid carbon formation. The polarization resistance of fuel electrode has different effects on the conversion ratios of CO2 and H2O under different conditions, which is obvious at low temperatures and high polarization resistance of fuel electrode. The conversion ratios of CO2 and H2O under limiting electrolysis condition decrease from 9.8 % to 36.6 %–1.8 % and 8.5 % when the polarization resistance of fuel electrode increases from 0 to 0.1 Ω cm2 at the H2O/CO2 ratio of 1:2 and 773 K.

Pyrolysis gas from biomass and plastics over X-Mo@MgO (X = Ni, Fe, Co) catalysts into functional carbon nanocomposite: Gas reforming reaction and proper process mechanisms

The metal catalysts X-Mo@MgO (X = Ni, Fe, Co) was studied as excellent catalyst for catalytic pyrolysis conversion of biomass and plastics into functional carbon nanocomposite. The proper reaction mechanism of the process was explored through the gas composition, and explored the bactericidal performance of functional carbon nanocomposite. The results showed that the Ni, Fe and Co-based catalysts elevated H2 gas yield reached to 57%, 34% and 44% as the addition of Mo, due to Mo or its oxide species for scission of small molecule compound. The introduction of NiMo@MgO catalyst produced lower CH4, and higher H2 and MWCNTs, which indicated that the formation of MWCNTs is mainly attributed to CH4 dehydrogenation. As a comparison, FeMo@MgO catalyst for CO disproportionation reaction could generate more MWCNTs and lower H2. The functional carbon nanocomposite from FeMo@MgO catalyst were comprehensively evaluated by multiple characterizations. TPO and Raman results confirmed that FeMo@MgO catalyst can provide an excellent carrier to generate MWCNTs with few defects and high graphitization. The functional carbon nanocomposite were initially applied to E.coli extinguishing. The core-shell structure catalyst not only has excellent bactericidal performance, but also has strong resistance to metal leaching.

Removal of hydrogen chloride from simulated coal gasification fuel gases using honeycomb-supported natural soda ash

In this study, we examined the HCl absorption performance of cheap natural soda ash loaded on a honeycomb support as a hot-gas cleanup method. Air-blown and oxygen-blown coal gasification fuel gases were used to simulate the gas composition. The effect of fuel gas composition on the HCl removal performance of the prepared absorbent was studied. It was found that the removal performance in an inert atmosphere was maintained in the presence of H2. On the other hand, the performance deteriorated in the presence of CO due to carbon deposition from the disproportionation reaction of CO. When CO2 was added to the CO, carbon deposition was suppressed in the air-blown gas and the HCl removal performance recovered. The performance recovery for an oxygen-blown gas was smaller than that for an air-blown gas. However, when the amount of CO2 added to the oxygen-blown gas was increased, the removal performance improved. The HCl removal performance of the absorbent was dependent on the initial HCl concentration and treatment temperature in the following order: 2000 ppm < 1000 ppm < 500 ppm, and 400 °C < 600 °C ≈ 500 °C. Recycled absorbents were prepared by loading natural soda ash once again on the recovered honeycomb supports that had been washed with water. Their HCl removal performance was similar to the fresh absorbent regardless of air-blown or oxygen-blown gasification. Thus, honeycomb supports were recyclable.

Carbon deposition behaviors in dry reforming of CH4 at elevated pressures over Ni/MoCeZr/MgAl2O4-MgO catalysts

Carbon deposition is a major bottleneck for the development of durable catalysts applicable for the dry reforming of CH4 (DRM). In this work, the carbon deposition behaviors in dry reforming of CH4 at elevated pressures over Ni/MoCeZr/MgAl2O4-MgO catalysts which exhibited a durable stability and excellent coking resistance at atmospheric pressure DRM reaction in our previous report were examined. The differences in the types and sources of carbon deposition under atmospheric pressure and elevated pressure were clarified by XRD, TPO, TEM and Raman spectroscopy as well as the comparative experiments conducted in CH4, CO and CH4/CO atmospheres. It was found that the stability of the catalyst declined rapidly at elevated reaction pressure, and the sources and types of carbon deposition in DRM reaction under atmospheric pressure and pressurized conditions were significantly different at temperatures above 800 °C, but barely differed at temperatures below 700 °C. Under atmospheric pressure, the filamentous carbon (carbon nanotubes, CNTs) was produced by CH4 decomposition reaction and CO disproportionation reaction at 500 and 600 °C, the encapsulated graphitic carbon was generated by CH4 decomposition reaction at 800 and 850 °C, and the filamentous carbon and encapsulated graphitic carbon deriving from CH4 decomposition reaction and CO disproportionation reaction coexisted at 700 °C. Under high pressure, CH4 decomposition reaction and CO disproportionation reaction were jointly involved in the formation of carbon deposition. The filamentous carbon was formed regardless of the reaction temperature, and accompanied by the encapsulated graphitic carbon at 700, 800 and 850 °C. It is concluded that stable DRM catalysts at atmospheric pressure may not be competent for the pressurized DRM because the sources and types of carbon deposition at pressurized conditions are different and the methods of carbon removal and suppression at atmospheric pressure are not fully applicable, thus further study is needed to develop durable catalysts at pressurized DRM.

Tunable CO Dissociation Assisted by H2 over Cobalt Species: A Mechanistic Study by In‐situ DRIFTS

AbstractFischer‐Tropsch synthesis (FTS) is an important heterogeneous catalytic process that can effectively reduce human dependence on the non‐renewable petroleum resources. Cobalt is a crucial active metal center in most catalysts, which effectively catalyzes syngas into valuable products such as liquid fuels. On this basis, we systematically investigated the adsorption of CO on the surface of different cobalt species and its dissociation characteristics assisted by H2 are studied by the in‐situ DRIFTS. For the metallic cobalt phase, H2‐assisted CO dissociation not only possessed the FTS activity, but also inhibited the CO disproportionation reaction. However, for the CoO phase, the bidentate carbonate species were decomposed into CO2. In addition, CoO presented a high‐chain propagation ability than that of Co under the same operation conditions. Co2O3 and Co3O4 also exhibited similar CO dissociation patterns with the assistance of H2. However, different from CoO phase, formate species also formed under the H2 atmosphere over these two Co species. In summary, CO dissociation would be well tuned via the assistance of H2 as demonstrated by the in‐situ DRIFTS. This work provides a new sight on the rational design of efficient cobalt catalysts toward the FTS processes.

Dry reforming of methane over Ni/Ce0.8Ti0.2O2-δ: The effect of Ni particle size on the carbon pathways studied by transient and isotopic techniques

The effects of Ni particle size (dNi ∼ 22–45 nm) of Ni/Ce0.8Ti0.2O2-δ on the carbon paths in the dry reforming of methane at 750 °C have been investigated by various transient and isotopic experiments. The aim was to provide new insights for improving catalyst’s coke-resistance. Various correlations have been derived between dNi and (i) the initial kinetic rates (per Ni particle) of CH4 dissociation and CO disproportionation reactions along with their respective amounts of carbon accumulation, (ii) the integral rates of CH4 conversion and CO formation and the amount of carbon deposition in the DRM, and (iii) the rate of carbon removal by lattice oxygen of support compared to that by oxygen formed via the CO2 activation route during DRM. The former rate was found larger than the latter one independent of dNi (nm). CH4 dissociation is the exclusive route of inactive carbon formation during DRM independent of dNi.

Deactivation Mechanism of Palladium Catalysts for Ethanol\t\t\tConversion to Butanol

A Pd/Al2O3 catalyst (Pd = 0.1 wt\t\t\t\t\t%) for ethanol conversion to butanol deactivates within 10 h of service, despite\t\t\t\t\tits high initial activity at 275°C. Probable deactivation mechanisms were\t\t\t\t\texplored, including poisoning of\t\t\t\t\t\tPd/Al2O3 due to adsorption of\t\t\t\t\tby-products on Pd, sintering of Pd phases, leaching of Pd from the catalyst,\t\t\t\t\tchanges in the Pd electronic state, changes in the catalyst’s porous structure,\t\t\t\t\tand blockage of Al2O3 active\t\t\t\t\tsites. The Pd/Al2O3 deactivation\t\t\t\t\twas found to be mainly caused by CO molecules that evolved during side\t\t\t\t\treactions. These molecules can either block Pd active sites due to the formation\t\t\t\t\tof strong Pd–CO complexes, or enter a CO disproportionation reaction to form\t\t\t\t\tcarbon deposits on Pd phases. The knowledge gained from this study can be used\t\t\t\t\tfor the targeted modification of\t\t\t\t\t\tPd/Al2O3 and the creation of\t\t\t\t\tselective systems operating stably in the presence of by-products.

Selective growths of single‐walled carbon nanotubes from mesoporous supports via CO disproportionation

AbstractMesopore‐confined cobalt catalysts are prepared to control diameters and chirality of single‐walled carbon nanotubes (SWCNTs) via CO disproportionation. Here, we demonstrate four synthetic strategies of growing semiconducting as well as metallic SWCNTs catalyzed by the cobalt nanoparticles with defined locations and sizes. Co‐condensation (catalyst‐1,3) processes provide constrained environment for small catalysts that grow uniform diameters (0.82–0.83 nm) of (7,5) and (8,4) semiconducting SWCNTs. Alternatively, surface‐grafting (catalyst‐2) and ion‐exchange processes (catalyst‐4) provide spacious mesopores toward formation of poly‐dispersed catalysts that grow a mixture of SWCNTs with wide‐range diameter distributions (0.83, 1.2–1.34 nm). Raman and photoluminescence excitation rationally correlate Raman breathing mode vibration to individual chirality and diameters of these SWCNTs. Informative in situ X‐ray absorption experiments reveal H2‐pretreatment (300–700°C) effects toward different oxidation states, bond distances, and coordination numbers of the cobalt catalysts. The CO disproportionation (6 atm, 800°C) reaction provides suitable confined growth of SWCNTs via co‐condensation of cobalt catalysts into mesoporous materials.

Simultaneous production of aromatics-rich bio-oil and carbon nanomaterials from catalytic co-pyrolysis of biomass/plastic wastes and in-line catalytic upgrading of pyrolysis gas

An integrated process that includes catalytic co-pyrolysis of biomass/plastic wastes and in-line catalytic upgrading of pyrolysis gas were conducted to simultaneously produce aromatics-rich bio-oil and carbon nanotubes (CNTs). The influences of feedstocks blending ratio on the characteristics of bio-oil and CNTs were established. The reaction mechanism of carbon deposition during the system was also probed. The results showed that co-feeding plastic to biomass siginificantly enhanced the selectivity of monoaromatics (benzene, toluene, and xylene) from 5.6% for pure biomass to the maximum yield of 44.4% for 75.0% plastic ratio, and decreased naphthalene and its derivates from 85.9 to 41.7% correspondingly. The most synergistic effect on BTX selectivity occurred at 25% of plastic ratio. The multi-walled CNTs were successfully synethsized on Ni catalyst by utilizing prolysis gas as feedstocks. For pure biomass, the least CNTs yield with ultrafine diameters of 3.9–8.5 nm was generated via disproportionation reaction of CO which was derived from decarboxylation and decarbonylation of oxygenates on the ZSM-5 acid sites. With the rise of plastic ratio, sufficient hydrocarbons were produced for CNTs growth, endowing CNTs with long and straight tube walls, along with uniform diameters (~16 nm). The CNTs yield increased as high as 139 mg/g-cata. In addition, the decreased CO2 inhibited dry reforming with C1-C4 hydrocarbons and deposited carbon, avoiding excessive etching of CNTs. Thereby, high-purity CNTs with less defects were fabricated when plastic ratio was beyond 50% in the feedstock. The strategy is expected to improve the sustainability and economic viability of biomass pyrolysis.

Thermokinetic Model for the Formation and Oxidation of Carbon Nanoforms

A thermokinetic model for the formation and decomposition of layered carbon nanoforms (LCNFs) has been proposed. The model relies on the fundamental dependence of discrete temperature component in the CO (Boudouard–Meyer) disproportionation reaction. Reversible reduction–oxidation reactions for individual LCNFs superpose in the range 820–1070 K. The superposition of reaction package has two thermokinetic components: rapid (discrete) and slow (continuous). The rate vred/ox C of the continuous process is 10–8–10–7 mole/sec. The activation parameter Ea ox C of the first-order reaction (smoldering) has been determined as 35 ± 5 kJ/mole. The rate of rapid oxidation processes exponentially depends on temperature, and vred/ox C is 10–6–10–5 mole/sec in the range 1073–1473 K. The activation energies for oxidation (combustion) of most nanoforms are in the range ~173 ± 5 kJ/mole. The oxidation temperatures for carbon nanoforms have been found. The following carbon nanoforms are mainly synthesized or oxidized in a CO or oxygen atmosphere: nanoonions at 823 K, graphite nanoplatelets at 873 K, stacked nanofibers at 923 K, conical nanofibers at 973 K, coiled nanofibers at 1013 K, multiwall nanotubes at 1033 K, and single-wall nanotubes at 1173 K. Carbon polymerization is driven by free radicals. The polymerization is catalytically promoted by three types of primary paramagnetic carbon radicals with one to three free electrons. The concentrations of radicals represent superposed Gaussian curves on the promoter’s acceptor surface in the range 820–1070 K. Primary radicals give rise to three nanoforms: spherical, lamellar, and tubular. The reactions are reversible as a function of environment and temperature. When equilibrium precipitation of the LCNFs and ‘carbon sludge’ is achieved, the reaction package is eventually converted to a S-shaped curve similar to the temperature dependence of CO partial pressure. The chemical properties of nanoforms combine two topological interactions: peripheral hydrophilic and surface hydrophobic. The synthesis and up-stop-up oxidation procedures in the qualification and selective determination of carbon nanoforms in mixtures are discussed.

Pt-Assisted Carbon Remediation of Mo2C Materials for CO Disproportionation

Using the CO disproportionation (Boudouard) reaction as a probe reaction, an in-depth analysis of temperature-programmed pulse response data shows that the addition of Pt to Mo2C mitigates deactiva...

Study the reaction mechanism of catalytic reforming of acetic acid through the instantaneous gas production

In order to study the reaction mechanism of steam reforming of bio-oil, acetic acid was selected as the model compound and Ni/Al2O3 as the catalyst to carry out a series of experiments. Through the comparative analysis of instantaneous gases productions, composition of liquid phase products and carbon deposition, we can infer the reaction mechanism of acetic acid catalytic reforming and carbon deposition process. It is found that dehydrogenation reaction, water-gas shift reaction and methane (CHx) reforming reaction are the main source of H2, while [CHx] catalytic cracking reaction and CO disproportionation reaction lead to carbon deposition, furthermore carbon-steam gasification reaction can consume carbon deposition to a certain extent. Acetone is an important intermediate for carbon deposition, leading to rapid deactivation of the catalyst. By characterizing the catalyst after the reforming reaction, we consider that the formation of carbon deposition mainly includes two stages: the coating of active sites and the growth of fibrous carbon deposition. The carbon deposition on the surface of used-catalyst is 0.86%, which is mainly composed of the accumulated [CC] and [CC] bonds.

Temperature effect on the synthesis of iron–cobalt nano-particles using catalytic chemical vapor deposition of CO2 in thermo-gravimetric analyzer: Analytical and thermodynamic studies

Iron, cobalt and Fe–Co catalysts were prepared by conventional precipitation (co-precipitation for Fe–Co) method for the synthesis of nano-particles, using CO2 as the carbon precursor by catalytic chemical vapor deposition. Synthesis was done in a thermo gravimetric analyzer at different temperatures ranging from 450 °C to 1000 °C particularly for Fe–Co nano particles. Products were then evaluated using the FESEM, TEM, XRD and EDS analyses. Nano-particles of pebble-like shapes with some of conjoined shapes were observed at different temperatures for Fe, Co and Fe–Co. It was also observed that increase in temperature not only enhanced the size of the nanoparticles but it also led to a greater sphericity and crystallinity of the nanoparticles. For Fe–Co alloy, the dimensions of nanoparticles were found using FESEM to be 51 ± 1 nm, 54 ± 1 nm, 72 ± 1 nm and 165 ± 1 nm at 500, 600, 700, and 800 °C, respectively. TEM also shows similar results to that of FESEM. XRD results show that at lower temperature (500 °C), products are amorphous in nature but at higher temperature (800 °C), the peaks became much longer and sharper indicating the crystalline nature of Fe–Co nanoparticles. CO disproportionation reaction was discussed and equations for equilibrium constant and mole fraction ( yCO and yCO2) were developed. It was observed that CO decomposition is thermodynamically limited from 520 to 800 °C which led to carbon deposition on the catalyst as observed by the carbon presence in EDS, XRD and TEM images i.e. the encapsulation of thin layer of carbon on the Fe–Co particles.

Investigation of carbon formation on Ni/YSZ anode of solid oxide fuel cell from CO disproportionation reaction

A challenge in the operation of solid oxide fuel cells (SOFCs) with hydrocarbon fuels is carbon deposition on the nickel/yttria-stabilized zirconia (Ni/YSZ) anode. This paper investigated the carbon formation on Ni/YSZ anode of solid oxide fuel cell (SOFC) due to CO disproportionation reaction. The steady-state rates of carbon formation under different CO/CO2 gas compositions were measured at temperature range from 600°C to 800°C. Experimental results showed that the steady-state rate of carbon formation caused by CO disproportionation reaction cannot solely be expressed with temperature or CO/CO2 gas ratios. A kinetic model divides the CO disproportionation reaction into several stepwise reactions, among which one of the stepwise reactions, namely, the C‐O bond cleavage reaction, is considered as the rate-limiting step of the overall reaction. This kinetic model fits very well with the experimental results. Based on the kinetic model and experimental data, a steady-state rate equation of carbon formation in the process of CO disproportionation reaction was derived at the temperature from 600°C to 800°C on Ni/YSZ anode of SOFCs.

Correlating the Onset of CO Disproportionation to Surface Chemistry on Ceria

Recycling carbon dioxide into carbon monoxide as a feedstock for industry and transportation has become of great interest as a means to reduce the impact of humanity on the environment. Due to the high thermodynamic efficiency inherent in electrochemical reduction of CO2 at high temperatures (~800 oC), solid oxide electrolysis (SOE) is an attractive method for CO production. Furthermore, in steam and CO2 co-electrolysis, the hydrogen and CO products constitute syngas, of significant importance to industry. Additionally, SOE of CO2 is actively being explored by the National Aeronautics and Space Administration (NASA) to generate O2 for future missions to Mars. Mitigating degradation of SOE cell performance over time remains a key challenge of the technology. For example, carbon accumulation from CO disproportionation reaction (coking) on the cathode during reduction of CO2, particularly problematic in dry conditions, leads to mechanical and electrochemical degradation of the cell. Other degradation modes, well known in the solid oxide fuel cell community, such as large electrode volume changes during redox with subsequent mechanical failure are also of concern. As a result, electrodes have been developed to counter these degradation modes in electrolysis and fuel cell operation. The majority of studies have largely been guided by empirical evidence indicating coke tolerant electrodes. In this presentation, we describe an investigation into the relationship between gas/solid interface compositional and operational factors that lead to the onset of coking. In situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) was used to evaluate conditions leading to coking using CO/CO2 mixtures at 300 mTorr total pressure at 450 oC. Electrical bias was applied to ceria based films, deposited using pulsed laser deposition on “buried” Pt electrodes, supported on ionic conducting substrates of yttria stabilized zirconia (YSZ) to in situ drive the CO2 reduction reaction. With electrochemical APXPS, we tracked the evolution of surface chemical change during coking reaction on ceria thin film samples with different dopant types (Zr, Gd) and doping concentrations. The surface spectroscopy analysis yielded information about the relationship between onset of coking, surface defect concentration (e.g., oxygen vacancies), surface composition (e.g., relative cation and impurity), and area specific resistance. During CO disproportionation, or coking, surface Ce3+ concentration was only loosely correlated with the deposited carbon intensity and indicated a threshold amount of Ce3+ for coking onset. The observed threshold phenomenon deepens previous understanding of Ce3+ sites’ catalytic role in CO disproportionation since no carbon was observed even considerable surface cerium had been reduced. By combining Monte Carlo simulation, we have shown that the Ce3+−Ce3+ pair formation exhibited similar behavior against surface Ce3+ concentration as coking intensity, indicating that Ce3−Ce3+ pair could be the dominant catalytic structure for coking reaction on ceria surface. These new insights on coking mechanism would be beneficial for rational coking-resistant electrodes design for CO2 electrolysis devices.

Laboratory astrochemistry: catalytic reactions of organic molecules over olivine-type silicates and SiC

AbstractA series of catalytic reactions has been performed in our laboratory using olivine-type silicates (OTS) and SiC as catalysts for the conversion of carbon-containing molecules (such as acetylene, CO and methanol) to small organic molecules (C2H4, C3H3, CH3O) and also polycyclic aromatic hydrocarbons (PAHs). Experimentally, small-to-medium-sized gas-phase compounds such as PAHs, reaction intermediates and hydrocarbon compounds were detected in situ using the time-of-light mass-spectrometry technique. Solid deposition on the catalyst surface was examined by high-resolution transmission electron microscopy and thermo-gravimetric analysis techniques. Our laboratory results show that the conversion of acetylene to PAHs, the CO disproportionation reaction for producing CO2 and carbon deposition (graphitic and carbon nanostructures), and also the transformation of methanol to hydrocarbon compounds can easily be achieved with OTS as a catalyst. Furthermore, the conversion of acetylene to PAHs could also be achieved by SiC as the catalyst. It is proposed that these catalytic reactions mimic similar chemical processes in circumstellar envelopes (CSEs).

Co-Cu-CaO catalysts for high-purity hydrogen from sorption-enhanced steam reforming of glycerol

High-purity hydrogen is usually produced through increasing inventory of CO2 sorbents in the sorption-enhanced steam reforming (SESR) processes. Herein, we report an effective approach to the high-purity hydrogen from SESR of glycerol by modifying a bi-functional Co-CaO catalyst to suppress the methanation side-reaction, which significantly consumes hydrogen. Bimetallic Co-based catalysts containing Ni, Cu and Zn were prepared from hydrotalcite-like materials as precursors. Over the 10Co-5Cu catalyst, the highest hydrogen purity up to 99.27% could be reached. Through temperature programmed desorption, oxidation, hydrogenation and CO disproportionation reactions, it was revealed that copper suppressed the formation of active coke species and CO methanation, thus alleviated the hydrogen consumption to allow for the production of high-purity hydrogen through SESR of glycerol.

The features of the CO disproportionation reaction over iron-containing catalysts prepared by different methods

The peculiarities of the CO disproportionation reaction over iron-containing catalysts have been studied. The reaction is known to be reversible and resulting in a direct path to the formation of carbon deposits and CO2. The iron-containing catalysts (1–5 wt% of Fe) were prepared by three different methods: co-precipitation of Fe- and Al-containing precursors, impregnation of γ-Al2O3 support with iron nitrate, and solution combustion synthesis (SCS). The latter technique is based on self-propagating combustion of active component precursor with fuel additive deposited on surface of fiberglass. The synthesized samples were characterized with physicochemical methods and tested in CO disproportionation reaction within the temperature range of 120–600 °C. The co-precipitated catalyst 5 wt% Fe–Al2O3 showed the highest activity (45 % conversion of CO) which is much superior to that observed for other catalysts in this reaction. According to SEM, CO disproportionation reaction has resulted in carbon deposition in both amorphous and nanostructured forms. It was shown that preparative technique has significant effect on catalytic performance of iron-containing catalysts.

Experimental Investigation of Carbon Deposition on a Ni/YSZ Anode of Solid Oxide Fuel Cell

The carbon depositions on a Ni/YSZ anode of solid oxide fuel cell (SOFC) with different gas ratios of CH4+H2 and CO+CO2 gas mixtures were experimentally studied. The carbon deposition rates for methane cracking and CO disproportionation were acquired at temperatures from 873K to 1073K. The kinetic models of the methane cracking and CO disproportionation reactions were verified by the experimental data. The results show that both the reactions of methane cracking and CO disproportionation are not solely related with the temperature or the gas mixture ratios. A kinetic model based on the elementary steps suggested by Alstrup fits well to the experimental data of methane cracking at the temperature range of 873-1073K. By assuming C-O bond cleavage as the rate-limiting step, a kinetic model of carbon deposition was derived for the CO disproportionation reaction and it is well fit to the experiments at temperature 973-1073K. The experimental results also show that the carbon deposition in the SOFCs is mainly due to the methane cracking reaction. Comparatively, the carbon deposition from CO disproportionation reaction is negligible.

Theoretical Study of Inorganic Carbonaceous Species Reaction with the Surfaces of BaTiO3(001)

Due to the variety of component elements and their high chemical stability at elevated temperatures, various perovskite oxide materials have been used to replace catalyst containing precious metals as oxidation catalysts or oxygen-activated catalysts (1). Additionally, because of their oxygen mobility through the material the C accumulation is not promoted. Such is the case of the resistance towards C deposition of Ni/BaTiO3-Al2O3 when employed as catalyst for low temperature dry reforming of CH4 (2). During the CH4 reforming, the C deposition is caused mainly due the CH4 decomposition or the CO disproportionation reaction that will lead to the formation of CO2 and C. On the other hand, one of the drawbacks of some perovskite materials such as BaTiO3 is that in the presence of CO2 the formation of a localized stable carbonate phase on the surface is possible (3). This carbonate phase will affect not only the catalytic activity of the material, but also may influence in its electronic properties. In this study the density functional theory (DFT) will be employed to analyze from a theoretical point of view the interaction of CO2 and the CO disproportionation reaction on the surfaces of BaTiO3(001). Our first approach with the BaO-terminated surface revealed that the CO molecule chemisorbs on the surface O atom. Additionally, if another CO molecule from the gas phase will interact with the already adsorbed CO molecule (Eley-Rideal reaction mechanism), the formation of trioxydehydroethene showed high spontaneity and the least stable but still probable to occur is the formation of CO2 and C that chemisorbs on top of an O atom (disproportionation reaction). Moreover, for the CO2 reaction with the BaO-terminated surface, the formation of CO3 anion showed to be quite stable. Furthermore, the CO2 reaction and CO disproportionation reaction will be also analyzed for the TiO2-terminated surface. References J. T. S. Irvine, in Perovskite Oxide for Solid Oxide Fuel Cells, T. Ishihara, Ed., p. 167, Springer, Fukuoka (2008).X. Li, Q. Hu, Y. Yang, Y. Wang, and F. He, Appl. Catal. A, 413– 414, 163, (2012).M. Wegman, L. Watson, A. Hendry, J. Am. Ceram. Soc., 87, 371 (2004).