Production of hydrogen from hydrogen sulfide assisted by dielectric barrier discharge

Hydrogen production by non-thermal plasma (NTP) assisted direct decomposition of hydrogen sulfide (H₂S) was carried out in a dielectric barrier discharge (DBD) reactor with stainless steel inner electrode and copper wire as the outer electrode. The specific advantage of the present process is the direct decomposition of H₂S in to H₂ and S and the novelty of the present study is the in-situ removal of sulfur that was achieved by operating DBD plasma reactor at ∼430 K. Optimization of various parameters like the gas residence time in the discharge, frequency, initial concentration of H₂S and temperature was done to achieve hydrogen production in an economically feasible manner. The typical results indicated that NTP is effective in dissociating H₂S into hydrogen and sulfur and it has been observed that by optimizing various parameters, it is possible to achieve H₂ production at 300 kJ/mol H₂ that corresponds to ∼3.1 eV/H₂, which is less than the energy demand during the steam methane reforming (354 kJ/mol H₂ or ∼3.7 eV/H₂).     

Effect of W incorporation on the product distribution in steam reforming of bio-oil derived acetic acid over Ni based Zr-SBA-15 catalyst

Zirconia incorporated SBA-15 type mesoporous material was synthesized following a one-pot hydrothermal route, characterized and used as the catalyst support in the synthesis of Ni and bi-metallic Ni–W based catalysts. Performances of these catalysts were tested in steam reforming of AcOH. Catalytic activity tests proved that the performances of SBA-15 and Zr-SBA-15 supported Ni based catalysts were highly stable and they also showed very high activity in steam reforming of acetic acid, giving complete conversion at temperatures over 700 °C. Product distributions were shown to be strongly influenced by the composition of the catalyst. In the case of 5Ni@Zr-SBA-15, syngas produced at 750 °C contained about 54% H₂, 22% CO, 20% CO₂ and 4% CH₄. These results indicated that decarboxylation reaction of AcOH to CH₄ and CO₂ was minimized over this catalyst. Results were considered to be highly promising for the production of hydrogen rich syngas. It was most interesting to observe that modification of this catalyst by the addition of tungsten caused significant changes in the product distribution. For instance, syngas produced over 5Ni-50W@Zr-SBA-15 at the same reaction conditions, contained equimolar quantities of H₂ and CO (about 47.5% each) with very small amounts of CO₂ and CH₄ (about 3% and 2%, respectively). Production of a syngas with such a composition was considered to be highly attractive from the point of view of a resource gas for dimethyl ether and Fischer-Tropsch synthesis.     

Influence of promoting Ni-based catalysts with ruthenium in the dry reforming of polypropylene plastics for syngas production

The catalytic dry reforming of plastic waste is conducted in two-stage fixed bed reactors. The pyrolysis of polypropylene plastics occurs in the first reactor, and the pyrolyzed gases undergo a reforming reaction with carbon dioxide over a catalyst in the second reactor. The wet impregnation method is used to synthesize Ru–Ni/Al₂O₃ catalysts, which are then calcined and reduced at 800 °C. The results show that as the nickel loading increases, the syngas production increases. Promoting the catalyst with a small quantity of ruthenium significantly improves the plastic conversion into syngas. The dry reforming of polypropylene over 1Ru15Ni/Al₂O₃ catalyst resulted in the maximum syngas yield (159 mmol_syngas/g_PP) at a 2:1 plastic to catalyst ratio. The catalytic dry reforming of plastics is promising for the production of synthesis gas.     

Synergistic catalysis of bi-metals in the reforming of biomass-derived hydrocarbons: A review

Biomass such as ethanol and glycerol has emerged as an alternative feedstock for hydrogen (H₂) production in recent years. Ethanol, which is high in H_2, can easily be derived from renewable biomass sources, whereas; glycerol is a by-product of biodiesel expected to be surplus in the coming years. Several catalytic reforming routes involving biomass such as steam, CO₂, auto thermal, partial oxidation and aqueous-phase reforming can produce syngas or H₂. Bimetallic catalysis is one of the potential solutions to reduce carbon formation and catalysts deactivation in reforming processes since it can produce more stable catalysts from the synergistic effect of the combined metals. There are many reviews on catalyst designs and reaction pathways reported in the literature; nevertheless, comparative literature is lacking on the metal configuration of bimetallic catalyst in biomass reforming particularly for ethanol and glycerol reforming reactions. Therefore, studies linked with the synergistic effects of various bi-metal combinations of catalysts used in biomass reforming processes have been reviewed in the paper. Moreover, the study provides data for the application of bimetallic catalyst for industrial biomass processes.     

Synthesis of NiO/MgO/ZrO2 catalyst for syngas production from partial oxidation and dry reforming of biogas

This work focuses on a facile NiO/MgO/ZrO₂ synthesis protocol for syngas production via partial oxidation and dry reforming of biogas. Herein, performance of the developed catalysts with different amounts of MgO (0–40 %wt. of support) and NiO (10–50 %wt.) on %CH₄ conversion, %CO₂ conversion, H₂/CO ratio, and carbon formation are studied. The results reveal the presence of monoclinic ZrO₂ and tetragonal ZrO₂ phases with 50%NiO/ZrO₂ catalyst synthesized by surface modification technique using carbon derived from urea. Addition of MgO in the catalyst shows ability to stabilize tetragonal ZrO₂ phase as well as enhance basic surface of the catalyst. These properties render the adsorption of CO₂ molecules on the surface, which subsequently are reduced by carbon, leading to CO production. Appropriated amount of NiO and MgO, which is 30 %wt. NiO and 20 %wt. MgO (relative to ZrO₂) can produce syngas having quality (H₂/CO molar ratio) of ca. 2.     

Reforming of methane and carbon dioxide by DC water plasma at atmospheric pressure

An experimental plasma chemical reactor, equipped with a novel water plasma torch, was used for reforming methane and carbon dioxide mixture to produce synthesis gas (syngas). Water plasma is generated by the torch at atmospheric pressure, in the absence of carrier gases, water cooling system and special steam supply system. The influence of the ratio of CO₂ to CH₄ and total feed gas rate on syngas production, composition and energy conversion efficiency were investigated. Compared to other plasma technologies, the higher reaction performance was obtained by the novel water plasma process. The results show that, under optimum experimental conditions, the energy conversion efficiency reaches up to maximum value of 1.87 mmol/kJ and the highest energy efficiency of 74.63% is achieved, which is higher than that of other plasma processes. Furthermore, the obtained syngas with high mole ratio of H₂ to CO (close to 2) is suitable for the direct industrial application.     

Thermodynamic analysis of syngas production from biodiesel via chemical looping reforming

In this study, thermodynamic analysis of the syngas production using biodiesel derived from waste cooking oil is studied based on the chemical looping reforming (CLR) process. The NiO is used as the oxygen carrier to carry out the thermodynamic analysis. Syngas with various H₂/CO ratios can be obtained by chemical looping dry reforming (CL-DR) or steam reforming (CL-SR). It is found that the syngas obtained from CL-DR is suitable for long-chain carbon fuel synthesis while syngas obtained from CL-SR is suitable for methanol synthesis. The carbon-free syngas production can be obtained when reforming temperature is higher than 700 °C for all processes. To convert the carbon resulted from biodiesel coking and operate the CLR with a lower oxygen carrier flow rate, a carbon reactor is introduced between the air and fuel reactors for removing the carbon using H₂O or CO₂ as the oxidizing agent. Because of the endothermic nature of both Boudouard and water-gas reactions, the carbon conversion in the carbon reactor increases with increased reaction temperature. High purity H₂ or CO yield can be obtained when the carbon reactor is operated with high reaction temperature and oxidizing agent flow.     

Desulfurization and tar reforming of biogenous syngas over Ni/olivine in a decoupled dual loop gasifier

For the production of bio-SNG (substitute natural gas) from syngas of biomass steam gasification, trace amounts of sulfur and tar compounds in raw syngas must be removed. In present work, biomass gasification and in-bed raw gas upgrading have been performed in a decoupled dual loop gasifier (DDLG), with aggregation-resistant nickel supported on calcined olivine (Ni/olivine) as the upgrading catalyst for simultaneous desulfurization and tar elimination of biogenous syngas. The effects of catalyst preparation, upgrading temperature and steam content of raw syngas on sulfur removal were investigated and the catalytic tar reforming at different temperatures was evaluated as well. It was found that 850 °C calcined Ni/olivine was efficient for both inorganic-sulfur (H₂S) and organic-sulfur (thiophene) removal at 600–680 °C and the excellent desulfurization performance was maintained with wide range H₂O content (27.0–40.7%). Meanwhile, tar was mostly eliminated and H₂ content increased much in the same temperature range. The favorable results indicate that biomass gasification in DDLG with Ni/olivine as the upgrading bed material could be a promising approach to produce qualified biogenous syngas for bio-SNG production and other syngas-derived applications in electric power, heat or fuels.     

Steam reforming of toluene as model biomass tar to H2-rich syngas in a DBD plasma-catalytic system

Biomass tar is one of the most troublesome issues limiting the further development of biomass pyrolysis and gasification. In this study, a plasma enhanced catalytic steam reforming technology was applied for biomass tar removal. Toluene was selected as biomass tar surrogate. The nano-sized alumina-supported nickel and iron catalysts with different molar ratios of M/Al (M: Ni or Fe, 0:1, 1:3, 1:1, 3:1, 1:0) were prepared for catalytic steam reforming of toluene in a non-thermal plasma reactor featuring dielectric barrier discharge (DBD). The results showed that syngas was the dominant gas product of toluene decomposition. The conversion efficiency of toluene and energy efficiency using Ni-Al and Fe-Al catalysts both followed a sequence: M1Al3 > M1Al1 > M3Al1, which is in line with the BET surface area and pore volume. However, the selectivity of H₂ and CO catalysed by Ni-Al and Fe-Al catalysts follows the order of M1Al3 < M1Al1 < M3Al1. Presumably, toluene dissociation is a process composed of adsorption-reaction-desorption. The formation of syngas is supposed to proceed as a series of ionic and free radical reactions occurring preferably in the gas phase. Ni1Al3 catalyst shows the largest potential in converting biomass tar into H₂-rich syngas, with a maximum toluene conversion of 96% and a largest H₂ yield of 2.18 mol/mol-toluene. Besides, the results showed that this hybrid plasma-catalysis system was potential in anti-carbon deposition.     

The assessment of reformation in a porous medium-catalyst hybrid reformer under excess enthalpy condition

A porous medium-catalyst hybrid reformer for hydrogen-rich syngas production by dry autothermal reforming (DATR) was investigated in this study. In the reforming process, the reaction under excess enthalpy was explored by visualization in packed-bed catalyst reactor. The hybrid design was arranged with a porous medium (PM) in the upstream of the catalyst packed-bed. In the arrangement, the reactants were preheated by internal heat recirculation and the selectivity of H₂-rich syngas was enhanced by the catalyst surface reaction. Controlled parameters included CO₂/CH₄ and O₂/CH₄ ratios, gas hourly space velocity (GHSV) with or without porous medium. The experimental results demonstrated that the reforming reaction with the hybrid reformer could achieve excess enthalpy under the tested parameters. The excess enthalpy ratio was between 0.15 and 0.55. The temperature measurement along the axial position and image observation of the catalyst packed-bed indicated that the flame was stably held at the interface of the PM and the catalyst bed, and this enhanced fuel conversion and reforming efficiencies, especially in the low methane conversion condition. In the dry autothermal reforming process, part of the chemical energy released from the reaction supplies the energy required for a self-sustaining reaction. Therefore, the selection of the parameters was determined to achieve high reforming efficiency and low energy loss percentage. The results showed that the energy loss percentage was between 12.7 and 24.6% and reforming efficiency was between 64.4 and 79.5% with the best reforming parameter settings (O₂/CH₄ = 0.7–0.9 and CO₂/CH₄ = 0.0–2.0).     

CO2 reforming of methane combined with steam reforming or partial oxidation of methane to syngas over NdCoO3 perovskite-type mixed metal-oxide catalyst

CO₂ reforming with simultaneous steam reforming or partial oxidation of methane to syngas over NdCoO₃ perovskite-type mixed metal oxide catalyst (prereduced by H₂) at different process conditions has been investigated. In the simultaneous CO₂ and steam reforming, the conversion of methane and H₂O and also the H₂/CO product ratio are strongly influenced by the CO₂/H₂O feed-ratio. In the simultaneous CO₂ reforming and partial oxidation of methane, the conversion of methane and CO₂, H₂ selectivity and the net heat of reaction are strongly influenced by the process parameters (viz. temperature, space velocity and relative concentration of O₂ in the feed). In both cases, no carbon deposition on the catalyst was observed. The reduced NdCoO₃ perovskite-type mixed-oxide catalyst (Co dispersed on Nd₂O₃) is a highly promising catalyst for carbon-free CO₂ reforming combined with steam reforming or partial oxidation of methane to syngas.     

Hydrogen production from partial oxidation of methane over dielectric barrier discharge plasma and NiO/γ-Al2O3 catalyst

Hydrogen production from partial oxidation of methane under the combination of dielectric barrier discharge (DBD) plasma and NiO/γ-Al₂O₃ catalyst with cordierite honeycomb monoliths as substrate was investigated. The results showed that obvious synergistic effect was generated between DBD plasma and catalyst. Compared with the DBD plasma reactor without catalyst, the CH₄ conversion and H₂ yield increased from 60.1% and 21.3% to 83.6% and 28.4%, respectively. When the discharge power is above 70 W, the combination of DBD plasma and NiO/γ-Al₂O₃ catalyst promotes partial oxidation of methane. The catalyst was characterized by X-ray diffraction (XRD). NiO on the surface of catalyst was reduced to Ni because of the introduction of DBD plasma. The activity of catalyst at low temperature was improved, and the generation of oiliness by-products was significantly reduced.     

A review on glycerol reforming processes over Ni-based catalyst for hydrogen and syngas productions

The rapid increase in energy demand coupled with the depletion of fossil-based resources has elevated the need for cleaner, renewable and sustainable fuels. Amongst alternative energies, hydrogen-based energy solution has become a promising replacement candidate due to its clean emission, high efficiency and it is considered to be a perfect substitute to reduce the dependency on non-renewable sources. Recently, the valorization biomass has become one of the attractive routes for hydrogen production and it has received growing attentions from worldwide researchers. Glycerol, the by-product from the biodiesel production faced oversupply crisis due to the high refining cost and this has affected the economics and sustainability of biodiesel industry. Hence, the most attractive way to boost the economic value of biodiesel is through the valorization of crude glycerol into value-added products, i.e., H₂ and syngas. Previously, the production of H₂ from glycerol has been carried out using various reforming processes such as aqueous phase reforming, pyrolysis, steam reforming, partial oxidation and dry reforming reactions. In the large scale industrial applications, Ni-based catalyst has been reported as the most common catalyst used in reforming reactions since this type of catalyst is readily available, inexpensive and possesses high catalytic activity. Ni was also found to have a good intrinsic activity and easily dispersed over the support materials. Throughout the years, various production routes and catalyst design have been reported in literature; however, none of the literatures are specifically focusing on benefits, constraints, limitation and challenges faced by glycerol reforming reactions catalyzed by Ni-based catalysts. Therefore, the focus of this review is to highlight the recent findings on Ni-based thermochemical processes of glycerol reforming reactions and emphasis will be given on the recent advances in catalyst and reactor designs as well as discovering the main routes of catalyst deactivation.     

Enhancement of plasma-assisted catalytic CO2 reforming of CH4 to syngas by avoiding outside air discharges from ground electrode

This work presents the effects of the insulation of ground electrode and operating parameters on CO₂ reforming of CH₄ to syngas in a coaxial-cylindrical dielectric barrier discharge (DBD) plasma reactor coupled with Ni/α-Al₂O₃ catalyst. For the conventional plasma reactor, abnormal outside discharge inevitably ignites and develops from the ground electrode, giving rise to the formation of harmful substances (e.g., NO_x) and the waste of energy. The power dissipation for the conventional reactor therefore includes both that used for the dry reforming reactions and the loss of energy due to the air discharge. The new finding of this work is that by covering the ground electrode with an insulating oil jacket, not only the NO_x formation is prevented but also the conversion rates, product selectivity and energy efficiency are largely enhanced by roughly 30, 10 and 100% at a specific energy input of about 47 kJ, respectively. The results are associated with the extinguishment of the discharge occurring outside the reactor, which is usually neglected when designing DBD reactors.     

Methanation over Ni/SiO2: Effect of the catalyst preparation methodologies

We confirmed here that the catalyst preparation methodologies have a significant effect on the activity and stability of Ni/SiO₂ catalyst for methanation of syngas (CO + H₂). Catalyst characterizations using X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and transmission electron microscope (TEM) were performed to investigate the structure and performance of the catalysts. The activity and stability of catalysts prepared by thermal decomposition and dielectric-barrier discharge (DBD) plasma decomposition of nickel precursor were compared. The plasma decomposition results in a high dispersion, an enhanced interaction between Ni and the SiO₂ support, as well as less defect sites on Ni particles. Enhanced resistance to Ni sintering was also observed. In addition, the plasma prepared catalyst effectively inhibits the formation of inactive carbon species. As a result, the plasma prepared catalyst exhibits significantly improved activity with enhanced stability.     

Recent advances in biogas upgrading to value added products: A review

It is undeniable that oil and gas explorations are going on at a frantic pace due to excessive fossil fuel usage across the world. This has compelled us to explore isolated or even uninhabited places to meet the surging demand for oil and gas. There is no doubt that scientists and researchers worldwide are exploring more renewable energy sources to produce value-added products. In the last few years, biogas' usage as a reactant gas in the catalytic reforming process has emanated as an energy carrier to produce energy-efficient products, i.e., syngas and methanol. This review aimed to analyze the research works focusing on the biogas DR reactions and methanol production from biogas. The findings of some experimental studies have been presented in the form of graphs for important selective parameters as case studies. The overall impression from the review suggests that the performance of the reforming catalysts deteriorates regarding different operating conditions. Still, the improvement in syngas production has been reported by neglecting the effect of H₂S impurity. Furthermore, various parameters have been discussed paragraphically to evaluate the catalytic performance in biogas dry reforming reactions and a check on catalyst synthesis methods. After that, a few scattered studies have been discussed on methanol synthesis using biogas as a feedstock.     

Methane reforming with carbon dioxide over a Ni/ZiO2–SiO2 catalyst: Influence of pretreatment gas atmospheres

Carbon dioxide reforming of methane to synthesis gas was studied over Ni/ZrO₂–SiO₂ catalyst under different pretreatment atmospheres. Characterization using powder X-ray diffraction, H₂ temperature-programmed reduction, H₂ temperature-programmed hydrogenation, TG/DTA, XPS, Raman spectra and transmission electron microscopy techniques revealed that gas atmospheres employed in the catalyst pretreatment have a significant influence on the catalytic performance. The helium-pretreated catalyst was found to be the most suitable catalyst for this application, showing the improved catalytic performance. More specifically, helium pretreatment facilitated the generation of well-distributed active metal sites while the heterogeneity of Ni components upon H₂ pretreatment degraded catalytic activity of metal sites considerably. Pretreatment under CO atmosphere resulted in the formation of carbon encapsulated metal species thus causing catalyst deactivation severely. Inefficient reduction under CH₄ activation and the presence of a great amount of carbonaceous species, disfavor the production of synthesis gas during the dry reforming.     

H2S effect on dry reforming of biogas for syngas production

The effect of hydrogen sulfide (H₂S) on dry reforming of biogas for syngas production was studied both experimentally and theoretically. In the experimental work, the H₂S effect on Ni‐based catalyst activity was examined for reaction temperatures ranging from 600°C to 800°C. It was found that the presence of H₂S deactivated the Ni‐based catalysts significantly because of sulfur poisoning. Although bimetallic Pt‐Ni catalyst has better performance compared with monometallic Ni catalyst, deactivation was still found. The time‐on‐stream measured data also indicated that sulfur‐poisoned catalyst can be regenerated at high reaction temperatures. In the theoretical work, a thermodynamic equilibrium model was used to analyze the H₂S removal effect in dry reforming of H₂S‐contained biogas. Calcium oxide (CaO) and calcium carbonate (CaCO₃) were used as the H₂S sorbent. The results indicated that H₂S removal depends on the initial H₂S concentration and reaction temperature for both sorbents. Although CO₂ was also removed by CaO, the results from equilibrium analysis indicated that the dry reforming reaction in the presence of CaO was feasible similar to the sorption enhanced water‐gas shift and steam‐methane reforming reactions. The simulation results also indicated that CaO was a more preferable H₂S sorbent than CaCO₃ because syngas with an H₂/CO ratio closer to 2 can be produced and requires lower heat duty.     

Zeolite and clay based catalysts for CO2 reforming of methane to syngas: A review

The development of coke and heat resistant catalyst for dry reforming of methane (DRM) is the major bottleneck towards the industrialization and commercialization of the process. Zeolite-based and clay-based catalysts are promising candidates for DRM to produce syngas (CO and H₂). The abundance, low cost, excellent properties and environmentally friendly nature of these support materials are an added advantage. Herein, this review entails the recent advances in development of zeolite and clay-based catalysts for DRM. In addition, the review captured a discussion on emerging trends in engineered mesostructured DRM catalysts. Tailoring of their framework configuration, pore architecture, crystals morphology and incorporation of active phases have led to the discovery of novel, robust and high-performance catalysts. Notably, advances recorded in the catalysts synthesis procedures and characterization methods were also highlighted and elaborately discussed. It is expected that this review provide a comprehensive roadmap in the quest for an economically and industrially potent catalyst for syngas production via DRM.     

Hydrogen production by steam reforming of methane over nickel based structured catalysts supported on calcium aluminate modified SiC

Steam reforming of methane (SRM) is an immensely important process for the production of hydrogen and syngas (H₂, CO). Ni-based alumina supported catalysts are conventionally used in the SRM process, but the coke formation and sintering are still challenging problems to develop an economical process. It was reported that the Lewis basicity of the support obviously plays a crucial role to prevent the coke formation, and basic supports such as calcium aluminate (CA_x) has shown superior resistance for carbon deposition, but in case of CA_x the major drawback is low thermal conductivity.In this work, in order to improve the catalytic performance of SRM, the Nickel based structured catalysts supported on the modified calcium aluminate (CA_x) with silicon carbide (SiC) were prepared. All synthesized catalysts were characterized by various techniques including N₂-physisorption, XRD, H₂-TPR, XPS, CO₂-TPR, TGA, TPH, and thermal conductivity analysis. It was found that the CA_x play an important role obtaining higher hydrogen yield and improved resistance to the carbon deposition. Even though, the methane conversion and H₂ yield efficiency for Ni supported on SiC modified CA_x/Al₂O₃ (NASC) catalyst was slightly lower than NAS and NAC catalysts, which caused by the weak interaction of active metal, but the NASC catalyst showed superior resistance to the coke formation compared to other catalysts. It was concluded that NASC catalysts is a promising candidates for the production of hydrogen by the steam reforming of methane.