Oxygen removal from syngas by catalytic oxidation of copper catalyst

The syngas from biomass gasification may contain trace oxygen besides of gaseous hydrocarbons, which will result in the temporarily or even permanently deactivation of Fischer–Tropsch (F–T) catalysts. In this paper, CuO–CeO₂/Al₂O₃ catalyst was developed to efficiently remove the trace oxygen from biomass syngas. The experimental results demonstrated that CuO–CeO₂/Al₂O₃ catalyst was considerably effective in removing oxygen to the level of below 1 ppm, its lifetime and deoxygenation capacity were 160 h and 3000 ml/g, respectively. Moreover, the optimum conditions of CuO–CeO₂/Al₂O₃ catalyst were 200 °C, 3.45 × 10⁵ Pa, and 3000 h⁻¹ gas hourly space velocity.     

Activity and selectivity enhancement of silica supported cobalt catalyst for alcohols production from syngas via Fischer-Tropsch synthesis

Synthesis of mixed alcohols together with clean fuels from syngas via Fischer-Tropsch synthesis is an attractive route for the utilization of coal, natural gas and biomass. In this work, a monometallic cobalt catalyst (Co/SiO₂-EOAM) was synthesized by impregnation using ethanolamine modified silica pellet as support and employed for the conversion of syngas. The combustion of carbon and nitrogen species during the calcination of catalyst facilitated the interaction between cobalt and support, which promoted the cobalt dispersion while inhibited the reduction of cobalt oxide. The Co/SiO₂-EOAM catalyst exhibited much higher activity and selectivity to alcohols compared to un-modified silica supported cobalt catalyst (Co/SiO₂). The higher activity was resulted from the improved cobalt dispersion. The co-existence of abundant metallic cobalt and Co²⁺ species were responsible for the increasing of alcohols selectivity.     

Biomass-derived syngas production via gasification process and its catalytic conversion into fuels by Fischer Tropsch synthesis: A review

The Fischer–Tropsch (FT) synthesis has been investigated over decades as an alternative route to obtain synthetic fuels from synthesis gas. FT is a high-performance synthesis based on metallic catalysis, mainly using ruthenium, cobalt and iron catalysts, which converts syngas in hydrocarbons and chemical precursors. This work presents a review on the aspects of the syngas production from biomass gasification and its subsequent conversion into fuels through the Fischer-Tropsch synthesis. The usage of biomass, including lignocellulosic residues, as a raw material in the gasification process. Biosyngas is highlighted as a synthetic fuel source to replace nonrenewable, conventional fossil fuels. Lignocellulosic material must be considered a low-cost feedstock to the liquid biofuel production on a large scale. Studies on syngas cleaning to attain the purity required by the FT process is revised. Recent understanding of reaction kinetics and thermodynamics has contributed to increasing the FT performance and economic viability. This paper includes also the debate on main catalysts, industrial process requirements, and chemical reaction kinetics and mechanisms of Fischer–Tropsch synthesis.     

Effect of zinc source on the ethanol synthesis from syngas over a slurry CuZnAl catalyst

Three CuZnAl catalysts were prepared with three kinds of zinc sources including zinc nitrate, zinc oxide, zinc carbonate by a complete liquid method, their catalytic performances were investigated and the structures were characterized by XRD, BET, TPR, NH₃-TPD, FT-IR, TEM and XPS. The results show that three catalysts own the ability to direct production of ethanol and higher alcohols from syngas, which occur at not any additives. It is found that a stronger electron transfer from Zn to Cu and Al occurred more in CAT-T and CAT-X, prepared with zinc carbonate and zinc nitrate, than CAT-Y with zinc oxide, which can cause the reduction of ZnO in part, producing oxygen deficiency species Zn^(2−δ) that are associated with the ability of growing carbon chain. CAT-Y shows a comprehensive advantage.     

Effect of mesoporous ZSM-5 morphology on the catalytic performance of cobalt catalyst for Fischer-Tropsch synthesis

Mesoporous ZSM-5 with various morphologies loading cobalt were prepared and applied in Fischer-Tropsch synthesis. Smaller ZSM-5 particles showed higher intensity of strong acid sites resulting in higher cobalt-support interaction. The activity and CH₄ selectivity were remarkably related with cobalt-support interaction over such acidic supports. Cobalt loaded on spindle mesoporous ZSM-5 exhibited the lowest activity and the highest CH₄ selectivity due to the strongest cobalt-support interaction, but the highest activity was obtained over cubic mesoporous ZSM-5 with the lowest cobalt-support interaction originating from weaker acid sites. In addition, adjusting acid intensity and mesopore volumes could successfully tuned hydrocarbon distribution. Spherical ZSM-5 with hierarchical structure containing larger mesopore volumes and moderate acid intensity effectively promoted the production of C₁₂-₁₈ hydrocarbons. The highest C₅-₁₁ selectivity was observed over cobalt supported on hexagonal meso-ZSM-5 due to the enhancement in diffusion limitation over lower mesopore volumes and hydrocracking of primary hydrocarbons over higher Brønsted acid sites.     

Investigation of alkaline complexant on ethanol synthesis from syngas over slurry CuZnAlOOH catalyst

A series of alkaline complexants promoted slurry CuZnAlOOH catalysts were prepared by a complete liquid-phase method. These catalysts were applied in a slurry bed reactor to selectively convert syngas into ethanol and higher alcohols (HAs). Herein, we showed that the addition of alkaline complexant remarkably enhanced both CO conversion and selectivity toward to ethanol and HAs in terms of ternary CuZnAlOOH catalyst. Besides, the formation of dimethyl ether (DME) was significantly suppressed. Interestingly, different from the traditional alkalis modified copper-based catalysts, these catalysts promoted by alkaline complexants mainly increased selectivity for ethanol, while not isobutanol. It also reduced the deactivation rate of the catalysts. These catalysts were comprehensively characterized by XRD, H₂-TPR, NH₃-TPD-MS, N₂ adsorption, FT-IR, XPS and TEM techniques. It was found that the increase of ethanol selectivity was related to the decrease of catalyst surface acidity, while the decrease of surface Cu⁺/(Cu⁰+Cu⁺) was regarded to the main reason for the catalysts deactivation. This paper showed that the introduction of alkaline complexants into Cu-based catalysts exhibited the potentiality to improve the stability and the yield of ethanol in a slurry bed reactor.     

Effect of non-metal promoters on higher alcohols synthesis from syngas over Cu-based catalyst

A series of non-metal promoted Cu-based catalysts were prepared and tested for the synthesis of higher alcohols from syngas in slurry bed reactor. The catalysts were characterized by XRD, ²⁷Al-MAS-NMR, H₂-TPR, NH₃-TPD, CO₂-TPD, TG-DTG and XPS techniques. Results showed that non-metal promoters mainly adjusted the acidity/basicity and the Cu content on catalysts surface, which played an important role in higher alcohols formation. Activity results showed that the syngas could be directly catalyzed to higher alcohols over CuZnAl catalyst. Also, it was found that acidic tartaric acid (TA) promoted methanol synthesis, whereas alkaline triethanolamine (TEA) favored the formation of C₂₊OH selectivity which reached approximately 48.0%.     

Kinetic modeling and reaction pathways for thermo-catalytic conversion of carbon dioxide and methane to hydrogen-rich syngas over alpha-alumina supported cobalt catalyst

This study investigates the kinetic modeling and reaction pathway for the thermo-catalytic conversion of methane (CH₄) and Carbon dioxide (CO₂) over alpha-alumina supported cobalt catalyst. Rate data was obtained from the thermo-catalytic reaction at a temperature range of 923–1023 K and varying CH₄ and CO₂ partial pressure (5–50 kPa). The rate data was significantly influenced by the changes in the reaction temperature as well as the CH₄ and CO₂ partial pressure. To estimate the kinetic parameters, the rate data were fitted with five Langmuir-Hinshelwood kinetic models. The discrimination of the kinetic models using different parameters revealed that the Langmuir-Hinshelwood kinetic model with the assumption of CH₄ being associatively adsorbed on a single and CO₂ being dissociative adsorbed with bimolecular surface reaction best described the rate data. The analysis of the kinetic model using a non-linear regression solver results in activation energies of 15.88 kJ/mol, 36.78 kJ/mol, 65.51 kJ/mol, and 41.08 kJ/mol for CH₄ consumption, CO₂ consumption, H₂ production, and CO production, respectively. The thermo-catalytic reaction was influenced by carbon as indicated by the rate of carbon deposition which was mainly caused by methane cracking. The reaction pathway for the thermo-catalytic conversion of the CH₄ and CO₂ over the alpha-alumina supported cobalt catalyst can best be described as by CH₄ associative adsorption on the alpha-alumina supported cobalt catalyst single site and CO₂ dissociative adsorption with bimolecular surface reaction.     

Study of partial oxidation reforming of methane to syngas over self-sustained electrochemical promotion catalyst

A self-sustained electrochemical promotion (SSEP) catalyst is synthesized for partial oxidation reforming (POXR) of CH₄ to produce syngas (H₂ and CO) at a relatively low temperature ranging from 350 to 650 °C. The SSEP catalyst is comprised of 4 components: microscopic Ni/Cu/CeO₂ anode, La_0.9Sr_0.1MnO₃ cathode, copper as electron conductor, and yttria-stabilized-zirconia as oxygen ion conductor, which form microscopic electrochemical cells to enable the self-sustained electrochemical promotion for the POXR process. The SSEP catalyst exhibited much better catalytic performance in POXR of CH₄ than a Ni–Cu–CeO₂ catalyst and a commercial Pt–CeO₂ catalyst. The CH₄ conversion over the SSEP catalyst is 29.4% at 350 °C and reaches 100% at 550 °C and the maximum selectivity to H₂ is on the level of 90% at 450–650 °C under a GHSV of 42,000 h⁻¹. The mechanism of the SSEP is discussed.     

Study of ethanol dehydrogenation reaction mechanism for hydrogen production on combustion synthesized cobalt catalyst

Cobalt nanoparticles synthesized via solution combustion synthesis were used to study the decomposition mechanism of ethanol for hydrogen production. Thermodynamic studies were conducted on the synthesis of cobalt nanoparticles using cobalt nitrate as a metal precursor in presence of different reducing agents; hydrazine, glycine, urea and citric acid. Thermodynamic results along with experimental characterizations show that the type and amount of fuel influence the adiabatic combustion temperature and the gases released during synthesis process affecting nanoparticle size, porosity and microstructure. The synthesized nanoparticles were activated by passing H₂ at 300 °C inside the reaction chamber before being used for studying the reaction pathway of catalytic dehydrogenation of ethanol. These studies indicate that cobalt catalyst is selective for aldehyde and acetate species along with the formation of H_2, H₂O and CO₂. Production of methane was also observed on cobalt surface at 400 °C. The spent catalyst nanoparticles were characterized after the reaction using XRD, SEM and TEM to analyze the particle size and its morphology. Results indicate a growth in particle size due to sintering, and carbon formation on the catalyst surface due to coking during ethanol dehydrogenation reaction.     

Catalytic pyrolysis of rice husks for syngas production over Fe-based catalyst in a fixed-bed reactor

Rice husk (RH) was pyrolyzed in a fixed-bed reactor between 400 and 800°C with Fe-based catalysts and the outlet gases were analyzed online by gas chromatography. The results showed that Fe₂O₃ has a good catalytic activity in the pyrolysis. The influence of Fe₂O₃ catalyst was to convert RH to largely syngas. The concentration of H₂ increased with increasing temperature and could be released completely at 700°C with the addition of Fe₂O₃. The concentration of CH₄ was not affected, indicating that Fe₂O₃ had no effect on the methanation.     

Co@Ru nanoparticle with core–shell structure supported over γ-Al2O3 for Fischer–Tropsch synthesis

Co@Ru/γ-Al₂O₃ core–shell structure catalysts with Co/Ru different weight ratios are successfully prepared via surface displacement reaction. This novel route including reduction of Co core by NaBH₄ on the surface of γ-Al₂O₃ and then substitution of Co species with Ru species, the resultant of reduction of RuCl₃ precursor with N₂H₄. These catalysts are characterized with techniques X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HRTEM), N₂ adsorption/desorption (BET), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and Fourier transform infra-red (FTIR) of CO adsorbed. The characterization results confirm a uniform dispersion of Co@Ru nanoparticles with core–shell structure over γ-Al₂O₃. The core–shell Co@Ru/γ-Al₂O₃ catalysts show the remarkable catalytic activity towards Fischer–Tropsch synthesis (FTS) in comparison with Co/γ-Al₂O₃, which is related to special core–shell structure. These catalysts exhibited excellent abilities in the cases of increasing formation of long-chain hydrocarbons and suppressing selectivity to lighter hydrocarbons.     

Synthesis of fatty acid methyl esters via the methanolysis of palm oil over Ca3.5xZr0.5yAlxO3 mixed oxide catalyst

Novel mixed metal oxide catalyst Ca_3.5xZr_0.5yAl_xO₃ was synthesized through the coprecipitation of metal hydroxides. The textural, morphological, and surface properties of the synthesized catalysts were characterized via Brunauer–Emmett–Teller method, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy. The catalytic performance of the as-synthesized catalyst series was evaluated during the transesterification of cooking palm oil with methanol to produce fatty acid methyl esters (FAME). The influence of different parameters, including the calcination temperature (300–700 °C), methanol to oil molar ratio (6:1–25:1), catalyst amount (0.5–6.5 wt%), reaction time (0.5–12 h) and temperature (70–180 °C), on the process was thoroughly investigated. The metal oxide composite catalyst with a Ca:Zr ratio of 7:1 showed good catalytic activity toward methyl esters. Over 87% of FAME content was obtained when the methanol to oil molar ratio was 12:1, reaction temperature 150 °C, reaction time 5 h and 2.5 wt% of catalyst loading. The catalyst could also be reused for over four cycles.     

Low temperature conversion of syngas to ethanol in liquid phase over Fe modified CuZn catalyst: The promoting effect of Fe

Fe modified CuZn catalysts were prepared and first used for the low temperature ethanol synthesis from syngas in liquid phase. Fe greatly enhanced the CO dissociative adsorption and promoted the formation of C₂₊ alcohols. The role of Fe was dependent on the catalyst preparation method. The co-precipitation method enhanced the interaction between Fe and other components, which could control the CO dissociative desorption to terminate the carbon chain growth of alcohols at ethanol. The wetness impregnation method benefited the dispersion of iron species and the synthesis of methanol and butanol. As a result, the co-precipitation method prepared Fe modified CuZn catalyst with spinel structure exhibited excellent catalytic performance for the low temperature syngas hydrogenation to ethanol in liquid phase with an ethanol selectivity of 40.9%.     

Low-temperature catalytic conversion of greenhouse gases (CO2 and CH4) to syngas over ceria-magnesia mixed oxide supported nickel catalysts

Running dry reforming of methane (DRM) reaction at low-temperature is highly regarded to increase thermal efficiency. However, the process requires a robust catalyst that has a strong ability to activate both CH₄ and CO₂ as well as strong resistance against deactivation at the reaction conditions. Thus, this paper examines the prospect of DRM reaction at low temperature (400–600 °C) over CeO₂–MgO supported Nickel (Ni/CeO₂–MgO) catalysts. The catalysts were synthesized and characterized by XRD, N₂ adsorption/desorption, FE-SEM, H₂-TPR, and TPD-CO₂ methods. The results revealed that Ni/CeO₂–MgO catalysts possess suitable BET specific surface, pore volume, reducibility and basic sites, typical of heterogeneous catalysts required for DRM reaction. Remarkably, the activity of the catalysts at lower temperature reaction indicates the workability of the catalysts to activate both CH₄ and CO₂ at 400 °C. Increasing Ni loading and reaction temperature has gradually increased CH₄ conversion. 20 wt% Ni/CeO₂–MgO catalyst, CH₄ conversion reached 17% at 400 °C while at 900 °C it was 97.6% with considerable stability during the time on stream. Whereas, CO₂ conversions were 18.4% and 98.9% at 400 °C and 900 °C, respectively. Additionally, a higher CO₂ conversion was obtained over the catalysts with 15 wt% Ni content when the temperature was higher than 600 °C. This is because of the balance between a high number of Ni active sites and high basicity. The characterization of the used catalyst by TGA, FE-SEM and Raman Spectroscopy confirmed the presence of amorphous carbon at lower temperature reaction and carbon nanotubes at higher temperature.     

Production of hydrogen via steam reforming of acetic acid over Ni and Co supported on La2O3 catalyst

Nickel (Ni)-cobalt (Co) supported on lanthanum (III) oxide (La₂O₃) catalyst was prepared via impregnation technique to study the steam reformation of acetic acid for hydrogen generation by using one-step fixed bed reactor. Moreover, in order to specify the physical and the chemical attributes of the catalyst, X-ray diffraction (XRD), nitrogen physisorption, temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia and carbon dioxide (TPD-NH₃ and CO₂), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) methods were employed. The nitrogen physisorption analysis showed that the presence of Co on Ni/La₂O₃ improved the textural properties of the catalyst by increasing the surface area, the pore diameter and the pore volume of the catalyst. This improved the dispersion of metal particle and caused a reduction in the size of metal particle, and consequently, increased the catalytic activity, as well as the resistance to coke formation. On top of that, the condensation and the dehydration reactions during acetic acid steam reforming created carbon deposition on acidic site of the catalyst, which resulted in the deactivation of catalyst and the formation of coke. Besides, in this study, Ni/La₂O₃ contributed to a high acetic acid conversion (100%) at 700 °C, but it produced more coking compared to Ni–Co/La₂O₃ and Co/La₂O₃ catalysts.