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•Production of renewable CH4 & liquid hydrocarbon through decarboxylation of WCO.•92 % decarboxylation and 96.31 mole% CH4 yield were obtained using Ru0.5Ni11 catalyst.•Coke ...deposition was reduced while CH4 production was enhanced by Ru metal.
Hydrothermal decarboxylation is an effective method for converting triglycerides, such as waste cooking oil (WCO), into renewable liquid hydrocarbons. However, one of the major challenges in producing liquid hydrocarbons from WCO is catalyst deactivation due to coke deposition, which prevents the catalyst from actively participating in the reaction. Additionally, CO2, a greenhouse gas, is evolved during the decarboxylation reaction(s). Converting CO2 into a reusable fuel, such as CH4, can help to reduce the environmental impact and can be used for power generation, appliances, industrial applications, and transportation. Ru metal is a well-known methanation catalyst that enhances methanation reactions of carbon oxides to minimize CO2 or CO production. In this study, we proposed a one-step process for producing both liquid hydrocarbons and CH4 during hydrothermal decarboxylation of WCO using Ru-Ni-θ Al2O3 catalysts in a batch reactor system. We hypothesized that the addition of Ru (0.2 wt% and 0.5 wt%) onto a 11wt%Ni/θ Al2O3 catalyst would significantly reduce coke deposition and convert CO2 and CO into renewable CH4. Experimental results showed that 11wt%Ni/θ Al2O3 catalyst was more acidic and displayed a higher degree of decarboxylation (97 %) compared to 0.2 wt%Ru/11wt%Ni/θ Al2O3 (94 %) and 0.5wt%Ru/11wt%Ni/θ Al2O3 (92 %) catalysts. Meanwhile, 0.2wt%Ru/11wt%Ni/θ Al2O3 and 0.5wt%Ru/11wt%Ni/θ Al2O3 catalysts yielded 87.64 and 96.31 mol% of CH4 compared to 11wt%Ni-θ Al2O3 catalyst (35.32 mol%). Ru reduced acidity and increased the resistance to carbon deposition on the catalyst’s surface by significantly enhancing the methanation reaction.
Hydrogen-rich blast furnace is considered an advanced technology in the iron and steel industry for reducing carbon emissions at the source. The CO utilization is instead reduced due to the severe ...carbon deposition behavior after hydrogen enrichment. This paper quantitatively investigated the effect of CO–H2–H2O–N2 multi-component on carbon deposition behavior, and a formation mechanism of deposited carbon was proposed finally. The results revealed that the optimum temperature range for carbon deposition was about 470–900 °C, and the maximum rate of carbon deposition was reached at 550–700 °C. At 600 °C, the carbon deposition rate for 100%CO and 40%CO–60%N2 were 0.54 g/d and 0.13 g/d, respectively. The aggravating effect of H2 to carbon deposition was 5.2 times that of H2O. Whereas the carbon deposition will be constrained in low CO and high H2 environment. The SEM showed that the morphology of the deposited carbon was filamentous, its formation mechanism on the iron surface is: (a) Adsorption of gases on the iron surface, (b) Formation of Fe3C layer, (c) Deposition of graphite layer, (d) Decomposition of Fe3C layer, (e) Formation of Fe3C–Fe + C (diss.) catalytic particles, (f) Formation of filamentous carbon, (g) Carbon activity in metallic Fe-filamentous carbon.
•The temperature range for carbon deposition is 470–900 °C based on TG experiment.•Carbon deposition rate is quantified and greatly aggravated by H2.•Effect of temperature on carbon deposition is attenuated strongly by H2.•Effect of H2 and H2O on the morphology of deposited carbon is the opposite.•Structural parameters and formation mechanism of filamentous carbon is revealed.
Sintering resistance and stability are pivotal objectives in the design of dry reforming of methane (DRM) catalysts. This study delves into the impact of cerium (Ce) as a promoter on the catalytic ...performance of Co–La bimetallic catalysts. A novel CoLa-xCe/MA catalyst was synthesized using alumina as a support via the co-impregnation method. The investigation explores the influence of Ce introduction on the catalytic performance of CoLa bimetallic catalysts and their resistance to carbon deposition. The CoLa bimetallic catalyst augments the number of oxygen vacancies on its surface during the reaction process compared to Co-based monometallic catalysts, leading to enhanced resistance to carbon deposition. Nonetheless, CoLa bimetallic catalysts are prone to active site agglomeration and sintering during the reaction, resulting in diminished catalyst stability. The introduction of Ce effectively alleviates this issue by promoting electron transfer between Ce and Co, facilitated by strong interactions between Ce and Co species. This engenders the creation of more active Co2+ sites, thereby enhancing the activation of CH4 in the DRM reaction. XPS analysis reveals a subtle shift in the La spectrum after the introduction of Ce, indicating favorable interactions between La and Ce for enhanced catalytic performance. Moreover, the addition of Ce as a promoter significantly diminishes the presence of medium and strong basic sites on the catalyst surface, promoting the formation of more moderately basic sites conducive to the DRM reaction. This effectively enhances the catalytic capability to adsorb and activate CO2 as well as mitigate carbon deposition during the DRM reaction process.
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•Ce introduction enhances the catalytic performance of Co–La bimetallic catalysts.•The addition of Ce reduces strong basic sites on the catalyst surface.•Ce mitigates active site agglomeration and sintering, improving catalyst stability.•Ce promotes electron transfer between Ce and Co and improved activation of CH4.•CoLa–5Ce/MA catalyst showed better activity and stability.
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•Features an extensive discussion on dry reforming of methane (DRM) over perovskite derived catalysts.•Exsolution of active metal from the bulk during the reduction process, produces ...a highly dispersed metal/support system.•Partial metal substitutions alter the physicochemical properties and enhance the catalytic performance of the perovskites.•Overall, perovskites are very efficient DRM catalysts, however, scope for further investigations prevail.
Dry reforming of methane (DRM) is widely studied as one of the potential routes for syngas production from two greenhouse gases (CH4 & CO2) and can reduce the net emission of these gases if the energy used for it is derived from non-hydrocarbon source. Many conventional metal/support catalyst systems, though are highly active, deactivate within few hours due to surface coke deposition or sintering of the active metal clusters. In order to overcome these challenges and withstand the extreme operating temperatures of DRM, active metals can be incorporated into crystalline oxides like perovskites, pyrochlores, hydrotalcites and hexaaluminates. These metal-containing oxides, once the active metal is reduced, produce a highly dispersed active catalyst.
This review emphasizes the application of perovskite-derived catalysts in dry reforming of methane. Perovskites are crystalline oxides with general formula of ABO3, where A is generally a rare earth, alkaline earth or alkali metal cation while B is a transition metal cation. The exsolution process involved in the reduction of perovskite catalysts produces smaller size metal particles which in turn dictate the superior catalytic performance of these materials. Preparation methods, “A” and/or “B” site partial substitutions and additional use of high surface area supports (like mesoporous silicates and basic oxides) for dispersing perovskite catalysts, greatly influence the physicochemical and catalytic behavior of these perovskite derived catalysts. “A” site substitutions generally enhance the oxygen mobility in the perovskite structure by generating oxygen vacancies which suppress the carbon deposition, while bimetallic synergistic effects are produced by addition of a second metal at the “B” site which tend to increase the activity and stability of these catalysts. This review also includes a detailed discussion on the mechanism of DRM in perovskite derived catalysts.
In this work, the volume swelling and carbon deposition behavior of pellets under shaft furnace smelting conditions were studied. The research process on swelling reduction utilized an online ...detection imaging method to determine the volume changes of pellets. The results suggest that an increase in temperature and a higher proportion of carbon monoxide in the reducing gas contribute to an escalation in the swelling rate during pellet reduction. Carbon deposition induced by carbon monoxide primarily occurs at 750 °C, and the powdery carbon deposition products on the surface of the pellets change over time, transitioning from carbon to a mixture of carbon and iron carbide (Fe3C) to a mixture of carbon, Fe3C, and metallic iron. This study elucidated the behavior of pellets in the low-temperature reduction section during the shaft furnace smelting process, offering a technical foundation for shaft furnace smelting technology.
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•The volume change of the pellet during the hydrogen rich reduction process was observed using a real-time camera system.•Investigated the reasons for variations in pellet reduction swelling index under different gas mixtures.•Investigated the mechanism of carbon deposition on the surface of pellets with hydrogen-rich gases.•Investigated the evolution mechanism of carbon deposition products at different stages.
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•The plastic/biomass ratio were studied in co-gasification of biomass and plastics.•Syngas quality and natures of deposited coke was studied on Ni/γ-Al2O3 catalyst.•50% of plastic ...ratio had remarkable synergy on syngas and deposited coke production.•88 mg gfeedstock-1 of CNT in deposited coke was produced during co-gasification.
In order to improve the quality of syngas and regulate the deposited coke, co-gasification of biomass and polyethylene wastes without and with steam were investigated in a bench-scale fixed bed reactor, where the feedstock was pyrolyzed at the temperature of 600 °C followed by catalytic reforming at 800 °C over Ni/γ-Al2O3 catalyst. The influences of different biomass to plastic ratios in feedstock on the quality of gas products were analyzed by means of gas chromatography. The as-formed deposited coke was examined by TEM, Raman, FTIR and TPO analysis. The results showed a synergistic effect on both gas and tar yields when PE was co-fed to RH, especially at PE content of 50%. For higher PE content (>50%), the total gas and H2 decreased due to more chain hydrocarbons with relatively large molecular size derived from PE volatiles being more difficult to be cracked than oxygenates from pyrolysis of biomass. Two natures of the deposited coke were identified as amorphous carbon and multi-walled carbon nanotubes (CNTs). With increasing PE proportion, CNTs growth exhibited a denser distribution with uniform diameter (~18 nm) and longer tube walls extending to a few microns. In the absence of steam, amorphous carbons was the leading type in coke depositions. The introduction of steam improved the quality and purity of CNTs and decreased amorphous carbon remarkably, owning to a stronger interaction between steam and amorphous carbon rather than CNTs with high graphitization, leading to high CNTs proportion of 61.5%. A significant synergistic effect on the CNT growth was observed particularly for 50–75% of PE. The CNT-predominated deposited coke slowed down the deactivation rate of catalysts, thus producing positive impact to total gas production.
In the study presented herein, the catalytic activity and stability of a Ni catalyst supported on Y2O3–ZrO2 was examined for the first time in the glycerol steam reforming reaction and compared with ...a Ni/ZrO2. The addition of Y2O3 stabilized the ZrO2 tetragonal phase, increased the O2 storage capacity of the support and the medium strength acid sites of the catalyst, and although the Ni/Zr catalyst had a higher concentration of basic sites, the Ni/YZr presented more stable monodentate carbonates. Moreover, the Ni/YZr had substantially higher Ni surface concentration and smaller Ni particles. These properties influence the gaseous products’ distribution by increasing the H2 yield and selectivity and preventing the transformation of CO2 to CO, by inhibiting the reverse water gas shift (RWGS) reaction from taking place. For both catalysts the main liquid products identified were allyl alcohol, acetaldehyde, acetone, acrolein, acetic acid and acetol; these were subsequently quantified. The time-on-stream experiments showed that the Ni/YZr was more stable during reaction and had a higher H2 yield after 20 h (2.17 in comparison to 1.50 mol H2/mol C3H8O3, for the Ni/Zr). Extensive investigation of the carbon deposits showed that although lower amounts of coke were deposited on the Ni/Zr catalyst, these structures were more graphitic in nature and had fewer defects, which means they were harder to oxidize. Moreover, transmission electron microscopy (TEM) analysis showed that sintering of Ni nanoparticles during the reaction was significant for the Ni/Zr catalyst, as the mean particle diameter increased from an initial value of 48.2 to 67.9 nm, while it was almost absent on the Ni/YZr catalyst (the mean particle diameter increased from 42.1 to 47.4 nm).
•Y2O3 stabilizes the tetragonal ZrO2 and improves reducibility.•Y2O3 leads to higher Ni surface concentration and smaller Ni particles.•Y2O3 prevents Ni sintering and forms carbon with low crystallinity.•Ni/YZr reveals increased H2 yield, CO2 selectivity and high H2/CO ratio.•Ni/YZr more resistant to deactivation in comparison with the Ni/Zr.
Syngas production via dry reforming of methane (DRM) was experimentally investigated using Ni-based catalyst. Ni/Al2O3 modification with CeO2 addition and O2 addition in the reactant were employed in ...this study to suppress carbon deposition and to enhance catalyst activity. It was found that DRM performance can be enhanced using CeO2 modified Ni/Al2O3 catalyst due to CeAlO3 formation. However, an optimum amount of CeO2 loading exists to obtain the best DRM performance due to the decrease in specific surface area as the CeO2 loading increases. Without O2 addition, the reverse water-gas shift reaction plays an important role in DRM. It was found that CH4 conversion and CO yield were enhanced while CO2 conversion and H2 yield are decreased as the CO2 amount in feedstock increased in DRM. With O2 addition in the fed reactant, it was found that the methane oxidation reaction plays an important role in DRM. CH4 conversion can be enhanced by O2 addition. However, decreases in CO2 conversion and H2 and CO yields occurred due to greater H2O and CO2 productions from the methane oxidation reaction. The thermogravimetric analysis (TGA) results showed that CeO2 modified Ni/Al2O3 catalyst would have the lowest amount of carbon deposition when O2 is introduced into the reaction.
•Syngas production via dry reforming of methane (DRM) was experimentally studied.•CeO2 modification on Ni/Al2O3 catalyst was used to suppress the carbon deposition.•O2 addition in the reactant was used to suppress the carbon deposition.•DRM performance depends on the CeO2 loading in the Ni/Al2O3 catalyst.•Methane oxidation is the key reaction in DRM with O2 addition.
The dry reforming of biogas on a Ni catalyst supported on three commercially available materials (ZrO2, La2O3ZrO2 and CeO2ZrO2), has been investigated, paying particular attention to carbon ...deposition. The DRM efficiency of the catalysts was studied in the temperature range of 500–800 °C at three distinct space velocities, and their time-on-stream stability at four temperatures (550, 650, 750 and 800 °C) was determined for 10 or 50 h operation. The morphological, textural and other physicochemical characteristics of fresh and spent catalysts together with the amount and type of carbon deposited were examined by a number of techniques including BET-BJH method, CO2 and NH3-TPD, XPS, SEM, TEM, STEM-HAADF, Raman spectroscopy, and TGA/DTG. The impact of the La2O3 and CeO2 modifiers on the DRM performance and time-on-stream stability of the Ni/ZrO2 catalyst was found to be very beneficial: up to 20 and 30% enhancement in CH4 and CO2 conversions respectively, accompanied with a CO-enriched syngas product, while the 50 h time-on-stream catalytic performance deterioration of ∼30–35% on Ni/ZrO2 was limited to less than ∼15–20% on the La2O3 and CeO2 modified samples. Their influence on the amount and type of carbon formed was substantial: it was revealed that faster oxidation of the deposited carbon at elevated temperatures occurs on the modified catalysts. Correlations between the La2O3 and CeO2-induced modifications on the surface characteristics and physicochemical properties of the catalyst with their concomitant support-mediated effects on the overall DRM performance and carbon deposition were revealed.
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•Beneficial DRM activity and stability impact of La and Ce incorporation in Ni/ZrO2.•Particular emphasis is given to the amount and type of surface carbon formed.•The amount of deposited carbon is oxidized faster on modified samples.•The graphitization of deposited carbon increases linearly with temperature.
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