Efficient nickel-based catalysts for amine regeneration of CO2 capture: From experimental to calculations verifications

High heat duty is an urgent challenge for industrial applications of amine-based CO₂ capture. The temperature (>110°C) of carbamate breakdown in amine regeneration requires large energy consumption. In this work, we report a novel, stable, efficient, and inexpensive Ni-HZSM-5 catalyst to improve the CO₂ desorption rate and reduce the heat duty. The impregnation method was applied for varying nickel content in the catalysts from 2.16 to 9.80 wt% in HZSM-5. The catalysts were characterized by scanning electron microscope, X-ray powder diffraction, N₂ adsorption–desorption, inductively coupled plasma-optical emission spectrometry, ultraviolet-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, NH₃-temperature programmed desorption (TPD), Infrared spectroscopy of pyridine adsorption, and Fourier transform infrared spectroscopy. The catalytic performance was evaluated by CO₂ desorption of rich amine solvent at 90°C. It was found that the introduction of nickel increased the acid sites of catalysts compared with parent HZSM-5. This phenomenon plays a key role on improving the CO₂ desorption rate. The density functional theory (DFT) calculations successfully explain the catalytic performance. The catalytic activity associates with the combined properties of MSA × B/L × Ni²⁺. The 7.85-Ni-HZ catalyst presents an excellent catalytic activity for the CO₂ desorption: it increases the amount of desorbed CO₂ up to 36%, reduces the relative heat duty by 27.07% with the same reaction time, and possesses high stability during five cyclic tests. A possible catalytic mechanism for the Ni-HZSM-5 catalysts through assisting carbamate breakdown and promoting CO₂ desorption is proposed based on experimental results and theoretical calculations. Therefore, the results present that the 7.85-Ni-HZ catalyst significantly accelerates the protons transfer in CO₂ desorption and can potentially apply in industrial CO₂ capture.     

Experimental study on the solvent regeneration of a CO2‐loaded MEA solution using single and hybrid solid acid catalysts

The performance of a hybrid solid acid catalyst consisting of a physical mixture of γ‐Al₂O₃ and H‐ZSM‐5 in terms of the rate and heat duty for solvent regeneration (i.e., CO₂ stripping) of a CO₂‐rich MEA solution was compared with the individual performance of γ‐Al₂O₃, H‐ZSM‐5, and H‐Y solid acid catalysts using MEA (2–7 mol/L), with initial CO₂ loading of 0.5 mol CO₂/mol MEA at 378 K. It was observed that any catalyst significantly decreased the energy required for CO₂ regeneration. The performance of the catalysts investigated ranked as follows: γ‐Al₂O₃/H‐ZSM‐5 = 2/1 > γ‐Al₂O₃ > H‐ZSM‐5 > H‐Y if the process is in the lean CO₂ loading region whereas it was H‐ZSM‐5 > γ‐Al₂O₃/H‐ZSM‐5 = 2/1 > γ‐Al₂O₃ > H‐Y if the process is in the rich CO₂ loading region. These results highlight the joint dependence on Brønsted/Lewis acidity and mesopore surface area of heat duty for solvent regeneration. © 2015 American Institute of Chemical Engineers AIChE J, 62: 753–765, 2016     

Pd‐Ag/α‐Al2O3 Catalyst Deactivation in Acetylene Selective Hydrogenation Process

The selective hydrogenation of acetylene to ethylene over Pd‐Ag/α‐Al₂O₃ catalysts prepared by different impregnation/reduction methods was studied. The best catalytic performance was achieved with the sample prepared by sequential impregnation. A kinetic model based on first order in acetylene and 0.5th order in hydrogen for the main reaction and second‐order independent decay law for catalyst deactivation was used to fit the conversion time data and to obtain quantitative assessment of catalyst performances. Fair fits were observed from which the reaction and deactivation rate constants were evaluated. Coke deposition amounts showed a good correlation with catalyst deactivation rate constants, indicating that coke formation should be the main cause of catalyst deactivation.     

Effects of promoters on catalytic activity and carbon deposition of Ni/γ‐Al2O3 catalysts in CO2 reforming of CH4

Catalytic reforming of methane with carbon dioxide was studied in a fixed‐bed reactor using unpromoted and promoted Ni/γ‐Al₂O₃ catalysts. The effects of promoters, such as alkali metal oxide (Na₂O), alkaline‐earth metal oxides (MgO, CaO) and rare‐earth metal oxides (La₂O₃, CeO₂), on the catalytic activity and stability in terms of coking resistance and coke reactivity were systematically examined. CaO‐, La₂O₃‐ and CeO₂‐promoted Ni/γ‐Al₂O₃ catalysts exhibited higher stability whereas MgO‐ and Na₂O‐promoted catalysts demonstrated lower activity and significant deactivation. Metal‐oxide promoters (Na₂O, MgO, La₂O₃, and CeO₂) suppressed the carbon deposition, primarily due to the enhanced basicities of the supports and highly reactive carbon species formed during the reaction. In contrast, CaO increased the carbon deposition; however, it promoted the carbon reactivity. © 2000 Society of Chemical Industry     

Promoted Fe2O3‐Al2O3‐CuO Chromium‐Free Catalysts for High‐Temperature Water‐Gas Shift Reaction

Promoted Fe₂O₃‐Al₂O₃‐CuO (FAC) chromium‐free catalysts were prepared for high‐temperature water‐gas shift reactions and characterized by X‐ray diffraction (XRD), Brunauer‐Emmett‐Teller method (BET), temperature‐programmed reduction (TPR), and transmission electron microscopy (TEM) techniques. The catalytic results revealed that among the investigated promoted catalysts with Ce, La, Zn, Y, and Mn as promoters, the Mn‐promoted sample showed higher activity compared to the other promoted catalysts. Increasing the Mn content improved the surface area and catalytic activity. The FAC catalyst promoted with a high Mn content exhibited maximum activity and relatively high stability in high‐temperature water‐gas shift reaction.     

Optimization of Effective Sol‐Gel Parameters for the Synthesis of Mesoporous γ‐Al2O3 Using Experimental Design

Mesoporous nanocrystalline γ‐alumina was prepared by a template‐free sol‐gel method using aluminum ethoxide as precursor. Significant parameters, such as the water/aluminum ethoxide molar ratio, the pH of the solution, and the time and temperature of aging, were optimized by the Taguchi method to obtain γ‐alumina with a high surface area and pore volume. The influences of the main parameters on the catalytic performance of the prepared catalysts were investigated via dehydration of methanol to dimethyl ether in a fixed‐bed reactor. The catalysts were characterized by X‐ray diffraction, N₂ adsorption‐desorption, ammonia temperature‐programmed desorption, and scanning electron microscopy techniques. The results show that the aging temperature had a significant influence on the catalyst performance.     

Preparation of Highly Active Nickel Catalysts Supported on Mesoporous Nanocrystalline γ‐Al2O3 for Methane Autothermal Reforming

Autothermal reforming (ATR) of methane was carried out over nanocrystalline Al₂O₃‐supported Ni catalysts with various Ni loadings. Mesoporous nanocrystalline γ‐Al₂O₃ powder with high specific surface area was prepared by the sol‐gel method and employed as support for the nickel catalysts. The prepared samples were characterized by X‐ray diffraction, Brunauer‐Emmett‐Teller, temperature‐programmed reduction, temperature‐programmed hydrogenation, and scanning electron microscopy techniques. It is demonstrated that the methane conversion increased with increasing in Ni content and that the catalyst with 25 wt % Ni exhibited the highest activity and a stable catalytic performance in the ATR process, with a low degree of carbon formation. Furthermore, the effects of the reaction temperature, the calcination temperature, the steam/CH₄ and O₂/CH₄ ratios, and the gas hourly space velocity on the catalytic performance of the 25 % Ni/Al₂O₃ catalyst were investigated.     

CO2 Methanation on Nickel Catalysts Supported on Mesoporous High‐Surface‐Area MgSiO3

Nickel catalysts prepared on high‐surface‐area mesoporous MgSiO₃ were synthesized and applied in methanation of CO₂. N₂ adsorption analysis confirmed the presence of the mesoporous structure on the synthesized samples and revealed that the increase in nickel content resulted in a shift of the pore size distributions to smaller pore sizes. Temperature‐programmed reduction analysis illustrated an improvement in reducibility of the catalysts by a higher nickel content. Catalytic results indicated enhanced CO₂ conversion with the increase in nickel percentage up to 15 wt %. The catalysts with higher percentage of nickel provided lower CO₂ conversion and CH₄ selectivity. The %15Ni/MgSiO₃ catalyst exhibited high catalytic stability under optimized conditions.     

Structure and Catalytic Performance of Mg‐SBA‐15‐Supported Nickel Catalysts for CO2 Reforming of Methane to Syngas

A series of Mg‐modified SBA‐15 mesoporous silicas with different MgO contents were successfully synthesized by a simple one‐pot synthesis method and further impregnated with Ni. The Mg‐modified SBA‐15 materials and supported Ni catalysts were characterized by N₂ physisorption (BET), X‐ray diffraction (XRD), temperature‐programmed desorption of CO₂ (CO₂‐TPD), temperature‐programmed H₂ reduction (H₂‐TPR), and temperature‐programmed hydrogenation (TPH) techniques and used for methane dry reforming with CO₂. CO₂‐TPD results proved that the addition of Mg increased the total amount of basic sites which was responsible for the enhanced catalytic activity over the Mg‐modified Ni catalyst. The excellent catalytic stability of Ni/8Mg‐SBA‐15 was ascribed to less coking and higher stability of the Ni particle size due to the introduction of Mg.     

Simultaneous Adsorption of SO2, NO,and CO2 by K2CO3‐Modified γ‐Alumina

The simultaneous adsorption of SO₂, NO, and CO₂ on K₂CO₃‐modified γ‐alumina under different operating conditions was studied in a fixed‐bed reactor. The experimental results showed that the influence of a temperature increase on the simultaneous adsorption of the three gases was complex and different from the effects seen when both chemical adsorption and competitive adsorption existed. An increase in O₂ concentration and small amounts of water could enhance the adsorption of SO₂ and NO while the adsorption of CO₂ was not influenced. The breakthrough curves of the simultaneous adsorption experiments suggested that the investigated adsorbent may be a good candidate for the simultaneous adsorption of SO₂, NO, and part of the CO₂ while the adsorption capacity for CO₂ still needs to be enhanced.     

Co‐Metal Catalysts on SiO2‐TiO2 for Methanol Production from CO2 – Effect of Preparation Methods

The effect of quantity, composition, and different impregnation sequences on the catalytic properties of Cu‐Zn‐Al/SiO₂‐TiO₂ in the CO₂ hydrogenation for methanol production was investigated. The Cu‐Zn‐Al catalysts supported on SiO₂ and TiO₂ were prepared by incipient wetness impregnation. Then, their performances in CO₂ hydrogenation were tested under defined conditions. The composition variation of Cu and Zn catalysts resulted in a high methanol production for Cu catalysts with a higher content of Cu, which was the active site for CO₂ activation. Regarding the metal quantity of catalysts, a relatively low loading of co‐metal (Cu‐Zn‐Al) led to the maximum methanol yield when compared with higher loadings as a result of the largest surface area.     

Effects of Ga doping on Pt/CeO2‐Al2O3 catalysts for propane dehydrogenation

This paper describes catalytic consequencesThis paper describes catalytic consequences of Pt/CeO₂‐Al₂O₃ catalysts promoted with Ga species for propane dehydrogenation. A series of PtGa/CeO₂‐Al₂O₃ catalysts were prepared by a sequential impregnation method. The as‐prepared catalysts were characterized employing N₂ adsorption‐desorption, X‐ray diffrtaction, temperature programmed reduction, O₂ volumetric chemisorption, H₂‐O₂ titration, and transmission electron microscopy. We have shown that Ga³⁺ cations are incorporated into the cubic fluorite structure of CeO₂, enhancing both lattice oxygen storage capacity and surface oxygen mobility. The enhanced reducibility of CeO₂ is indicative of higher capability to eliminate the coke deposition and thus is beneficial to the improvement of catalytic stability. Density functional theory calculations confirm that the addition of Ga is prone to improve propylene desorption and greatly suppress deep dehydrogenation and the following coke formation. The catalytic performance shows a strong dependence on the content of Ga addition. The optimal loading content of Ga is 3 wt %, which results in the maximal propylene selectivity together with the best catalytic stability against coke accumulation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4365–4376, 2016     

Catalytic desorption of CO2-loaded solutions of diethylethanolamine using bentonite catalyst

The absorption of CO₂ gas into aqueous alkanolamine solutions is the most advanced CO₂ separation technology and a key challenge in this technique is the energy-intensive process of solvent regeneration. The tertiary amine N,N′-diethylethanolamine (or DEEA) is a candidate CO₂-capturing solvent with potential. To improve the energy efficiency of regeneration of DEEA, several catalysts were used for desorbing CO₂ from loaded solutions of DEEA (2.5 M) at T = 363 K. Desorption trials were conducted in batch mode. The initial CO₂ loading varied in the 0.3–0.35 mol CO₂/mol DEEA range. The performance was analyzed by calculating the rate of CO₂ desorption, cyclic capacity, and reduction in sensible energy. The amount of thermal energy needed for amine regeneration was significantly lowered by using nine transition metal oxide catalysts and the hierarchy was as follows: Al₂O₃ < MoO₃ < V₂O₅ < TiO₂ < MnO₂ < ZnO < Cr₂O₃ < SiO₂ < ZrO₂. Among the metal oxides, Al₂O₃ increased desorption efficiency compared to blank runs by 89%. A clay-based powder bentonite was also used as catalyst and its efficacy was compared with the metal oxides. This cheap and easily available bentonite catalyst was tuned through simple ion-exchange with four acids (HCl, H₃PO₄, HNO₃, and H₂SO₄). Upon treatment with H₂SO₄, bentonite remarkably increased desorption efficiency by 100%. Furthermore, bentonite catalyst treated with sulphuric acid (denoted here as Bt/H₂SO₄) was characterized by Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared spectrometery (FTIR), X-ray diffraction (XRD), and ammonia temperature-programmed desorption (NH₃-TPD). In this way, a comprehensive study on catalytic desorption of DEEA was performed.     

Catalytic Oxidation of CO over Nanocrystalline La1–xCexNiO3 Perovskite‐Type Oxides

Nanocrystalline La_1–xCe_xNiO₃ (x = 0.1, 0.3, 0.5, 0.7, 0.9) perovskite‐type oxide catalysts prepared by the Pechini method were employed in catalytic CO oxidation and the effect of substitution of La by Ce on CO conversion was evaluated. The results indicated the remarkable effect of La substitution with Ce on the catalytic performance at low temperatures. The reaction temperature had a significant influence on the stability of the catalysts. The La_0.1Ce_0.9NiO₃ sample exhibited the highest activity among the prepared catalysts in CO oxidation reaction. In addition, the influence of different parameters including pretreatment condition, feed ratio, and gas hourly space velocity (GHSV) on the catalytic performance was examined. The optimum catalyst proved high stability under severe reaction conditions in the presence of water vapor and CO₂ in the feed stream.     

Effect of the Mg/Al Atomic Ratio of Ni‐Mg‐Al Catalysts for the Hydrodealkylation of 1,2,4‐Trimethylbenzene

The hydrodealkylation of 1,2,4‐trimethylbenzene (1,2,4‐TMB) to benzene, toluene and xylenes (BTX) was investigated on Ni‐Mg‐Al catalysts prepared by the coprecipitation method. The catalytic performances of these catalysts were considerably influenced by the Mg content of the catalyst. The catalysts were characterized via X‐ray diffraction, H₂‐temperature‐programmed reduction, NH₃‐temperature‐programmed desorption (TPD), CO₂‐TPD, and Fourier transform infrared spectroscopy. The results demonstrated that the appropriate amount of Mg species significantly affected the structural properties and caused the Ni nanoparticles to become highly dispersed. The higher activity of the catalysts might be ascribed to the homogenous distribution of the Ni nanoparticles, and the synergetic effects between Ni⁰, NiAl₂O₄ and MgAl₂O₄ were the key factor for obtaining the BTX.     

Preparation of γ‐Fe2O3 Catalysts and their deNOx Performance: Effects of Precipitation Conditions

Magnetic γ‐Fe₂O₃ catalysts were prepared by microwave‐assisted coprecipitation utilizing the direct‐titrate and back‐titrate precipitation technique with different precipitants, namely, (NH₄)₂CO₃, NaOH, Na₂CO₃, and NH₄OH, which were evaluated in the selective catalytic reduction of NO_x with NH₃. The optimum γ‐Fe₂O₃ catalyst preparation method was direct titration with NH₄OH as the precipitant, which exhibits high deNO_x efficiency. This direct titration was effective to maintain the proper crystallization degree of γ‐Fe₂O₃, improve the pore structure, and suppress the formation of α‐Fe₂O₃ phase, being advantageous to get tiny and uniform discrete γ‐Fe₂O₃ particles with high activity in selective catalytic reduction. NH₄⁺‐based precipitants in direct titration leads to an increase of the surface O/Fe atom ratio, and more lattice oxygen sites are exposed to the crystal surface.     

Cr‐Doped La‐Ni‐O Catalysts Derived from Perovskite Precursors for CH4‐CO2 Reforming under Microwave Irradiation

The nickel catalysts derived from Cr‐doped LaNiO₃ perovskite‐like precursors were characterized by X‐ray diffraction, high‐resolution transmission electron microscopy, temperature‐programmed oxidation, temperature‐programmed reduction, and X‐ray photoelectron spectroscopy. Their catalytic performance in CO₂ reforming of methane under microwave irradiation was investigated. It was found that the structure and morphology of the oxide composites in this research were influenced by the ratio of Ni and Cr, and the mismatch of La³⁺, Ni³⁺, and Cr³⁺ may cause phase segregation. The catalytic performance of the Ni catalysts is dependent on the oxygen mobility of the perovskite oxide matrix, the content of the reduced Ni⁰, and the content of the remaining perovskite structure. The mobile oxygen in the perovskite matrix in the catalyst may enhance the conversion of CO₂ during the reaction.     

Investigation mechanism of DEA as an activator on aqueous MEA solution for postcombustion CO2 capture

In this work, Diethanolamine (DEA) was considered as an activator to enhance the CO₂ capture performance of Monoethanolamine (MEA). The addition of DEA into MEA system was expected to improve disadvantages of MEA on regeneration heat, degradation, and corrosivity. To understand the reaction mechanism of blended MEA‐DEA solvent and CO₂, ¹³C nuclear magnetic resonance (NMR) technique was used to study the ions (MEACOO^‐, DEACOO^–, MEA, DEA, MEAH⁺, DEAH⁺, , ) speciation in the blended MEA‐DEA‐CO₂‐H₂O systems with CO₂ loading range from 0 to 0.7 mol CO₂/mol amine at the temperature of 301 K. The different ratios of MEA and DEA (MEA: DEA = 2.0:0, 1.5:0.5, 1.0:1.0, and 0:2.0) were studied to comprehensively investigate the role of DEA in the system of MEA‐DEA‐CO₂‐H₂O. The results revealed that DEA performs the coordinative role at the low CO₂ loading and the competitive role at high CO₂ loading. Additionally, the mechanism was also proposed to interpret the reaction process of the blended solvent with CO₂. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2515–2525, 2018     

Production of Synthesis Gas via Dry Reforming of Methane over Co‐Based Catalysts: Effect on H2/CO Ratio and Carbon Deposition

The effect of support type on synthesis gas production using Co‐based catalysts supported over TiO₂‐P25, Al₂O₃, SiO₂, and CeO₂ was investigated. The catalysts were prepared by the incipient wet impregnation method and characterized by various techniques for comparison. Experiments were performed in a micro tubular reactor. The results revealed that all Co‐supported catalysts produced synthesis gas ratios of 1 and below and, thus, proved to be well‐suited for methanol and Fischer‐Tropsch syntheses. Co catalysts supported over TiO₂‐P25 and Al₂O₃ provided better synthesis gas ratios and stability performances. The promotion of a Co/TiO₂‐P25 catalyst with Ce had a substantial influence on its catalytic activity and the amount of carbon deposit. A Ce‐promoted catalyst diminished markedly the extent of carbon deposition and thus boosted the performance towards better activity and stability.     

Production of Higher Hydrocarbons from CO2 over Nanosized Iron Catalysts

The effects of the particle size of a Fe/Cu/K catalyst on CO and CO₂ hydrogenation reactions as well as the variation of crucial factors such as surface area and basicity, reduction, carburization, and catalytic behavior of precipitated Fe/Cu/K catalysts were evaluated. Hematite nanoparticle catalysts with various surface tensions were produced by homogeneous precipitation in alcohol/water solvents. The basicity of the K‐promoted iron catalyst was higher in iron catalysts with lower particle size. The increase in K‐basic sites at the surface of catalysts with smaller particle size was attributed to their higher surface areas. Elevation of catalyst basicity led to considerably stronger dissociative CO adsorption. Shifting the oxygen removal pattern to lower temperature was the consequence of faster nucleation of FeCx crystallites on promoted surface oxides. CO₂ hydrogenation can occur in two distinct direct and indirect routes via the Fischer‐Tropsch mechanism.