Reverse Boudouard Reaction Research Articles

Accumulation of the Carbonaceous Species on the Ni/Al2O3Catalyst during CO2Reforming of Methane

The dependency of the rate of <TEX>$CO_2$</TEX> reforming of methane on the catalyst loading and the reactor size was examined at a fixed temperature of <TEX>$750\;^{\circ}C$</TEX> and a fixed GHSV of 18000 mL(STP)/<TEX>$g_{cat}.h$</TEX>. The conversion of methane in <TEX>$CO_2$</TEX>reforming decreased with increase in the reactor size. The catalyst was severely deactivated with increase in the catalyst amount. The amount of carbonaceous species combustible below <TEX>$550\;^{\circ}C$</TEX>, determined by TPO experiments with the used catalyst samples increased with increase in the catalyst amount, which was again confirmed by XRD and TEM experiments. The increase of the carbonaceous species combustible below <TEX>$550\;^{\circ}C$</TEX> may be due to the suppression of the reverse Boudouard reaction, since the <TEX>$CO_2$</TEX> reforming of methane, a highly endothermic reaction, resulted in lowering the reaction temperature.

Kinetic Modeling for Methane Reforming with Carbon Dioxide over a Mixed-Metal Carbide Catalyst

A cobalt−tungsten η-carbide material [Co6W6C] was investigated as a precursor for a stable and active catalyst for the dry reforming of methane to produce synthesis gas. The kinetics of CH4/CO2 reforming were studied under differential conditions over a temperature range of 500−600 °C, based on a detailed experimental design. The observed rates qualitatively follow a Langmuir−Hinshelwood type of reaction mechanism. Such a scheme is considered quantitatively, with four reactions: methane reforming, reverse water-gas shift, carbon deposition, and carbon removal by a reverse Boudouard reaction. Of these, carbon deposition and carbon removal are generally disregarded in most of the reported kinetic models. The parameters of the model were successfully estimated for all of the experimental data. The comparison plots of the observed data and the predicted model show generally a good fit for all of the product species.

The Mechanistic Study of Methane Reforming with Carbon Dioxide on Ni/α-Al2O3

The reactions of oxidized and reduced 6 wt % NiO/α-Al2O3 with H2, CH4, CO2, O2, and their mixtures are studied in flow and pulse regimes using a setup equipped with a differential scanning calorimeter DSC-111 and a system for chromatographic analysis. It is shown that treatment with hydrogen at 700°С results in the partial reduction of NiO to Ni. Methane practically does not react with oxidized Ni/α-Al2O3 but it does react actively with the reduced catalyst to form H2 and surface carbon. The latter is capable of reacting with lattice oxygen of Ni/α-Al2O3 (slowly) and with adsorbed oxygen (rapidly). Carbon dioxide also reacts with surface carbon to form CO (rapidly) and with metallic Ni to yield CO and NiO (slowly). Thus, the main route of methane reforming with carbon dioxide on Ni/α-Al2O3 is the dissociative adsorption of CH4 to form surface carbon and H2 and the reaction of this carbon with CO2 resulting in the formation of CO by the reverse Boudouard reaction. Side routes are the interaction of the products of methane chemisorption with catalyst oxygen and the dissociative adsorption of CO2 on metallic nickel. A competitive reaction of surface carbon with adsorbed oxygen results in a decrease in the CO2 conversion in methane reforming with carbon dioxide. Therefore, the presence of gaseous oxygen in the reacting mixture decelerates methane reforming (catalyst poisoning by oxygen).

Methane Reforming with Carbon Dioxide on the Co/α-Al2O3 Catalyst: The Formation, State, and Transformations of Surface Carbon

The interactions of oxidized and reduced Co/α-Al2O3 (4 wt % CoO) with H2, CH4, CO2, and O2 and their mixtures are studied in flow and pulse regimes using a setup involving a DSC-111 differential scanning calorimeter and a system for chromatographic analyses. It is shown that treatment with hydrogen at 700°C results in the partial reduction of cobalt oxide to Co. Methane poorly reacts with the oxidized catalyst but readily reacts with the reduced catalyst to form H2 and surface carbon. The initial surface carbon transforms into other forms, which block the cobalt surface to different extents and differ in the heats of reaction with CO2. Carbon dioxide may react with the surface carbon to form CO (rapidly) and with metallic Co to form CO and CoO (slowly). Thus, the main route of methane reforming with carbon dioxide on Co/α-Al2O3 is the dissociative adsorption of CH4 to form surface carbon and H2 and the reaction of surface carbon with CO2 to form CO via the reverse Boudouard reaction.

Kinetics and mechanisms of the reverse Boudouard reaction over metal carbonates in connection with the reactions of solid carbon with the metal carbonates

The decomposition processes of alkali or alkaline earth carbonates with a large excess of carbon, and the reverse Boudouard reaction given by CO2/C→2CO over metal carbonates, were compared. The carbonates of Li+, Na+, K+, Cs+, Sr2+ and Ba2+ generated CO exclusively by an intermolecular redox reaction given by CO32-+C→2CO+O2-. The reverse Boudouard reaction over these metal carbonates at 700°C proceeded at a steady rate until just before the carbon was completely consumed, and in the cases of Li+, Sr2+ and Ba2+, the rates agreed with the initial rates of the intermolecular redox reaction. On the other hand, the rates over the carbonates of Na+, K+ and Cs+, the oxides of which undergo a disproportionation reaction to produce gas-phase metal and liquid-phase metal peroxide, were much higher than the initial rates of the intermolecular redox reaction. This discrepancy can be explained by the presence of a catalytic process on the metal-covered surface of the silica wool that was used for preventing the highly basic gas-phase metals from escaping.

Ｒｈ添加Ｖ２Ｏ５／ＳｉＯ２触媒によるＣ３Ｈ８の脱水素反応 ＣＯ２共存効果およびＲｈ添加効果

The dehydrogenation of C3H8 and the reduction of CO2 were carried out simultaneously using Rh-added V2O5/SiO2 catalysts. The addition of Rh to V2O5/SiO02 and the presence of CO2 in the reactant flow increased the yield of C3H6 at the steady state of the reaction. CO2 may be utilized as an oxidant for the reaction and/or may be used to remove produced carbon by reverse Boudouard reaction. In particular, the addition of very small amount of Rh (0.1 wt%) was effective to increase the effect of CO2 addition.

97/01140 Spouted-bed coal gasifier burner and its use in coal gasification

The possibility of using CO2 as a reactant for fuel production can remarkably improve its mitigation. Herein, an approach that comprises two steps, methane pyrolysis and Reverse Boudouard (RB) reaction in the presence of O2 was able to achieve H2/CO ratio in the range 1.5–2.4 and autothermic conditions by controlling the amount of CO2 that reacts in the presence of O2. This approach is highly flexible in the target products because it can operate in a large range of process parameters and each step occurs simultaneously in two independent reactors. Both steps were studied at the same temperature (750 °C and 800 °C) in several consecutive cycles. A multifunctional catalyst composed of alumina modified by nickel, vanadium, and lithium decomposed methane (10% in helium) with high selectivity into coke and hydrogen. This step was followed by the spent catalyst regeneration in a CO2 rich atmosphere in the presence of O2 producing initially mainly CO and then CO2, thus significantly improved the CO/CO2 separation. Moreover, at high temperature the CO2/O2 reacts in a proportion greater than one. By decreasing the coke in spent catalyst by just reducing the pyrolysis time, the CO2/O2 ratio increased remarkably.