Organo-modified mesoporous silica for sorption of carbon dioxide

Abstract  

Organo-modified mesoporous silica SBA-15 has been studied for sorption of carbon dioxide (CO₂). The SBA-15 sample was functionalized with a branched chain polymer, polyethylenimine (PEI), of different molecular weights (1,300 and 2,000 g mol⁻¹). Surface modification was carried out by impregnation of silica by PEI or by grafting with (3-chloropropyl)triethoxysilane, followed by substitution of chlorine atoms by PEI ligands. The prepared modified mesoporous materials were characterized by nitrogen adsorption/desorption at 77 K, high-resolution transmission electron microscopy, small-angle X-ray scattering, and thermal methods. Sorption of CO₂ was studied by gravimetric method at 303 K. The total amount of sorbed CO₂ varied between 0.19–0.67 mmol/g for respective samples. Regeneration of the materials after adsorption was achieved by thermal treatment at 343 K.     

Zeolite-supported Ni catalyst for methane reforming with carbon dioxide

In the present work, we compare the catalytic behaviour, in the dry reforming of methane, of Ni-based Silicalite-1 type catalyst obtained by different post-synthesis treatments. The Silicalite-1 type material, used as Ni-support, has been treated in order to observe the role of the silanol groups on the Ni impregnation, and then on the overall catalyst performance. Among the applied treatments (ionic-exchange, calcinations and silylation), the silylation is the one that allows the formation of smaller and more reducible Ni-oxide species that not only improve the methane conversion but also reduce the deactivation of the catalyst, due to the coke deposition.     

Ultra-stable Ni catalysts for methane reforming by carbon dioxide

Methane reforming by carbon dioxide has been studied over ultra-stable Ni catalysts. The catalyst was characterized by XRD, IR and TEM and temperature programmed hydrogenation. The nickel–magnesia solid solution catalyst containing low nickel has shown excellent stability (>3000 h) and no carbon deposition in the methane reforming by carbon dioxide. It was also found that the small nickel metal particle interaction with support surface is effective for the inhibition of carbon formation.     

Carbon deposition in methane reforming with carbon dioxide

Coke formation in the dry reforming of methane was studied using a thermobalance (TG) and with a catalytic microreactor in the temperature range 800–950 K. Silica-supported and lanthana-supported nickel catalysts were examined. The effects of process variables such as temperature and gas composition (He dilution, CH₄/CO₂ ratio) on the coke formation rate were determined. The reactivity of H₂ on several kinds of carbon was also investigated. The morphology of the coke was studied by scanning electron microscopy (SEM). The induction times for coke formation were significantly affected by temperature and by the CO content in the feed gas. The results of catalytic tests were consistent with the TG measurements. The behaviour of SiO₂ and La₂O₃ supported Ni catalysts agree with a mechanism in which the lanthana support plays an important role in the carbon deposition.     

The effect of alkaline earth metal oxide on nickel catalyst for carbon dioxide reforming of methane

A study on the effect of alkaline earth metal oxide on the activity and stability of nickel catalyst for carbon dioxide reforming of methane was performed. When CaO, SrO, and BaO were used as supports, there was no difference in catalytic activity between the catalysts made by coprecipitation and impregnation. However, when MgO was used as a support, the catalyst prepared by coprecipitation showed superior activity than that made by impregnation. The higher activity of the catalyst made by coprecipitation was due to the formation of solid solution consisting of nickel and magnesium. The formation of the solid solution enhanced the dispersion of nickel and the resistance to coke formation.     

Modeling carbon dioxide adsorption on polyethylenimine-functionalized TUD-1 mesoporous silica

Samples of porous, foam-like TUD (Technische Universit?t Delft)-1 mesoporous silica were functionalized with polyethylenimine and were used as a substrate for CO(2) adsorption. Produced solids were characterized by means of electron microscopy, thermogravimetric analysis, and N(2) adsorption/desorption at 77K, in order to prove that polymer chains efficiently filled the pores of functionalized samples. CO(2) adsorption isotherms on polyethylenimine-containing TUD-1 were evaluated at T=298, 313, 328, and 348 K for pressures up to 100 kPa by means of a volumetric technique. The CO(2) adsorption capacity proved to be significantly dependent on temperature, with the highest capacity encountered at T=348 K. The experimental data for CO(2) adsorption were satisfactorily described by means of the Langmuir isotherm, and the dependence of the isosteric heat on the fractional coverage of the adsorbent was evaluated by means of the van't Hoff equation, showing values in the order of 80 kJ/mol for a fractional coverage of about 50%.     

Effect of metal oxides on the reforming of methane with carbon dioxide

The effect of basic and rare earth metal oxides on the stability of nickel-based catalysts for the CO₂ reforming of CH₄ has been studied. The addition of metal oxides increased the stability of Ni-based catalysts and reversed the values of the reaction orders with respect to both CH₄ and CO₂. In the presence of metal oxides, the values of the reaction orders with respect to CO₂ partial pressure followed the same trend of catalyst stability.     

Effect of chemical modification on carbon dioxide adsorption property of mesoporous silica

Three adsorbents were prepared by different modification methods, which were grafting silica gel with (3-aminopropyl) trimethoxysilane, grafting silica gel with acrylamide polymer, and impregnating silica gel with acrylamide polymer, respectively. The characterization of materials was carried out by N(2) adsorption experiments, Fourier transform infrared spectroscopy, scanning electron microscopy, thermo-gravimetric analysis, and elemental analyses. The results showed that the amine group was successfully loaded on all three modified adsorbents; among that, the polymer-modified silica adsorbents had higher amine content and larger surface area than the aminopropyl-grafted silica adsorbent and displayed higher thermal stability than the other polymer-modified silica materials previously reported. The CO(2) adsorption/desorption experiments performed at 25°C by TGA-DSC method showed that the highest CO(2) adsorption capacity (0.98 mmol/g) was observed for the polymer-impregnated silica adsorbent. CO(2) adsorbed on all samples was completely desorbed by purging with inert gas at 60°C except for the aminopropyl-grafted silica material, which showed the highest enthalpy of CO(2) adsorption.     

Catalytic reforming of methane by carbon dioxide over nickel-exchanged zeolite catalysts

A series of nickel-exchanged catalysts based on ZSM-5, USY, and Mordenite zeolites has been prepared by the ionic exchange method. The NiZeol catalysts have been characterized by XRD and BET. The exchange levels and nickel contents of the catalysts have been determined by chemical analysis. The acidity of the zeolite supports has been investigated using NH₃ adsorption microcalorimetry. The number of acidic sites was found to decrease according to the following sequence: HUSY > HZSM-5 > HMOR. The temperature programmed reduction studies showed that the most reducible catalyst is NiZSM-5. The Ni-exchanged zeolites presented good catalytic performance in the methane reforming by CO₂. At a temperature of 650°C, CH₄ conversions of 71 and 54% were achieved on NiUSY and NiZSM-5 respectively. At 400°C, CO₂ FTIR adsorption has shown that CO₂ decomposes into CO and oxygen on NiZSM-5 which explains its reactivity at such a low temperature, while no decomposition of this probe molecule was observed on the NiUSY catalyst. The catalytic performance was found to vary in the following sequence at 650°C: NiUSY > NiZSM-5 > NiMOR. Moreover, the catalytic performances were found to depend strongly on the CO₂/CH₄ ratio in the feed and were markedly improved for CO₂/CH₄ greater than 1.     

纳米ZrO2的合成对负载Ni催化剂的CH4/CO2重整反应的影响

采用共沉淀法、醇热合成法和干法分别合成了纳米ZrO2（ZrO2 CP、ZrO2 ET和ZrO2 S）,用XRD、 BET、SEM等对其结构和表面性质进行表征,以CH4/CO2重整为探针反应研究了不同方法合成的纳米ZrO2负载Ni催化剂的催化性能,并与载体的物化性质进行了关联。实验结果表明,以干法合成的纳米介孔ZrO2 S具有较大的比表面积（133m2/g）和较好的孔径分布(4.9nm),Ni/ZrO2 S催化剂在CH4/CO2重整反应中表现出较好的催化性能。     

Assessment of the intrinsic interactions of mesoporous silica with carbon dioxide

Three mesoporous silica, SBA-16, SBA-15 and MCM-41, with different structures and porosities were synthesized via a hydrothermal method and their interactions with carbon dioxide (CO₂) were investigated through thermal programmed desorption (TPD) and differential scanning calorimetry. TPD measurements provided precise assessments of the intrinsic affinity towards CO₂, without the influence of moisture. All silica materials were found to exhibit intrinsic affinity towards carbon dioxide, but the surface basicity, expressed in terms of retained CO₂ amount, is markedly influenced by increases in pore size and framework structures. SBA-15 displayed the highest CRC values, explained in terms of larger pore size, lower numbers of acidic out-of plane Si–OH and higher numbers of much less acidic in-plane silanols. These findings provide valuable information for a better understanding of the role of the silica structure in the intrinsic basicity, prior to further modifications for improving the affinity towards CO₂ or merely for catalysis purposes involving CO₂ as reagents, intermediates or products.     

水热法制备Ni-Sm/SiC催化剂甲烷二氧化碳重整性能的研究

通过水热法制备了Ni-Sm/SiC催化剂（Ni的含量固定为9%，钐的含量固定为5%）。采用XRD、BET、ICP、H₂-TPR、TG-DTA和TEM等技术对催化剂进行表征。对催化剂在甲烷二氧化碳重整反应中的催化活性、不同镍前驱体的影响、催化剂的积炭行为进行了研究。研究结果表明，水热法制备的Ni-Sm/SiC催化剂有着优异的催化活性、稳定性和抗积炭能力。不同镍前驱体对催化剂的性能没有影响。     

Nickel catalysts supported on MgO with different specific surface area for carbon dioxide reforming of methane

In this paper, three kinds of MgO with different specific surface area were prepared, and their effects on the catalytic performance of nickel catalysts for the carbon dioxide reforming of methane were investigated. The results showed that MgO support with the higher specific surface area led to the higher dispersion of the active metal, which resulted in the higher initial activity. On the other hand, the specific surface area of MgO materials might not be the dominant factor for the basicity of support to chemisorb and activate CO₂, which was another important factor for the performance of catalysts. Herein, Ni/MgO(CA) catalyst with proper specific surface area and strong ability to activate CO₂ exhibited stable catalytic property and the carbon species deposited on the Ni/MgO(CA) catalyst after 10 h of reaction at 650 °C were mainly activated carbon species.     

Template in situ inducing dispersion of nickel on SBA-15 for methane reforming with carbon dioxide

Highly dispersed Ni/SBA-15 catalysts were prepared via template extraction with varying different extraction times (Ni/S-x, x = 0.5, 3.5, 6.5 h) for methane reforming with carbon dioxide. Based on the various characterization results and initial activity evaluation, Ni/S-3.5 h catalyst showed the best catalytic performance. Compared with the catalyst prepared via template calcination (Ni-S), Ni/S-3.5 h catalyst held steady with CH₄ and CO₂ conversions while those of the Ni-S catalyst respectively decreased by 15 and 11% during the long-term stability test at 700 °C for 50 h. As TEM and TG–DSC results confirmed, Ni particles in spent Ni/S-3.5 h catalyst stayed well-dispersed with size slightly increasing from an initial 3.9–4.1 nm and nearly no carbon deposition was observed. On the contrary, Ni-S catalyst was subjected to sintered metal particles (increased from 11.6 to 18 nm) and formed carbon fibers. The prominent resistance to sintering and coking over stable Ni/S-3.5 h catalyst was attributed to the high dispersion and strengthened metal-support interaction induced via the residual in situ templates.     

Supercritical carbon dioxide processing of fluorinated surfactant templated mesoporous silica thin films

The effect of processing mesoporous silica thin films with supercritical CO2 immediately after casting is investigated, with a goal of using the penetration of CO2 molecules in the tails of fluorinated surfactant templates to tailor the final pore size. Well-ordered films with two-dimensional hexagonal close-packed pore structure are synthesized using a cationic fluorinated surfactant, 1-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)pyridinium chloride, as a templating agent. Hexagonal mesopore structures are obtained for both unprocessed films and after processing the cast films in CO2 at constant pressure (69-172 bar) and temperature (25-45 degrees C) for 72 h, followed by traditional heat treatment steps. X-ray diffraction and transmission electron microscopy analysis reveal significant increases in pore size for all CO2-treated thin films (final pore diameter up to 4.22 +/- 0.14 nm) relative to the unprocessed sample (final pore diameter of 2.21 +/- 0.20 nm) before surfactant extraction. Similar pore sizes are obtained with liquid and supercritical fluid treatments over the range of conditions tested. These results demonstrate that combining the tunable solvent strength of compressed and supercritical CO2 with the "CO2-philic" nature of fluorinated tails allows one to use CO2 processing to control the pore size in ordered mesoporous silica films.     

Development of Cu foam-based Ni catalyst for solar thermal reforming of methane with carbon dioxide

Using solar energy to produce syngas via the endothermic reforming of methane has been extensively investigated at the laboratory- and pilot plant-scales as a promising method of storing solar energy. One of the challenges to scaling up this process in a tubular reformer is to improve the reactor's performance, which is limited by mass and heat transfer issues. High thermal conductivity Cu foam was therefore used as a substrate to improve the catalyst's thermal conductivity during solar reforming. We also developed a method to coat the foam with the catalytically active component NiMg_3AlO_x. The Cu foam-based NiMg_3AlO_x performs better than catalysts supported on SiSiC foam, which is currently used as a substrate for solar-reforming catalysts, at high gas hourly space velocity(≥400,000 mL/(g·h)) or at low reaction temperatures(≤ 720 °C). The presence of a γ-Al_2O_3 intermediate layer improves the adhesion between the catalyst and substrate as well as the catalytic activity.     

羟基磷灰石负载Ni催化剂中Ni含量对催化甲烷二氧化碳重整制合成气性能的影响

以低温沉淀方法制备的羟基磷灰石(HAp)为载体,采用浸渍法制备了一系列不同Ni含量的Ni/HAp催化剂,并采用BET、H2-TPR、XRD、SEM、FT-IR、TEM和TG-DTA技术对催化剂进行了表征。结果表明,NiO含量为13%的催化剂表现出最好的催化甲烷二氧化碳重整制合成气活性,在850℃、空速3.6×104mL/(h·gcat)的反应条件下,甲烷和二氧化碳的转化率在10 h内分别稳定在72%和83%。这主要归因于催化剂中金属和载体之间的强相互作用。虽然反应后的催化剂表面有少量的积炭,但这些积炭多以丝状炭存在,并不会影响催化剂的活性和稳定性。     

Application of non-thermal atmospheric pressure ac plasmas to the carbon dioxide reforming of methane

Methane conversions of 11.9%, yields of hydrogen as high as 23.3% and energy yields of 1.0 mol H₂/kWh have been achieved from CO₂ reforming of CH₄ in non-thermal, atmospheric pressure plasma reactors with Pt coated electrodes. Two reactors have been studied. A novel fan type reactor consisting of a movable rotor and immobile stator produced the highest yields in contrast to a tube type (silent discharge) reactor with a glass dielectric barrier. Conversions, yields of hydrogen and energy yields (expressed as mol H₂/kWh) were studied for CO₂/CH₄ concentrations of 1.1% and 5.0% in He as a function of flow rate and input voltage. Hydrogen yields are observed to increase as the input voltage is increased from 411 V to 911 V and the flow rate is decreased from 100 cc/min to 30 cc/min. Energy yields vary only slightly with input voltage and flow rate. Hydrogen yields show little dependence on CO₂/CH₄ concentrations, but energy yields are approximately five times greater for the 5.0% mixture than the 1.1% mixture. Selectivities to H₂, CO, coke, and low molecular weight hydrocarbons were also evaluated and compared to data obtained without CO₂ in the feed. Hydrogen selectivities of nearly 100% were obtained, with small amounts of ethane and propane as the only observed side products and the selectivites were approximately the same whether CO₂ was present or absent in the mixture. However, the reaction proceeds much more cleanly when CO₂ is present, producing CO. The syngas product has an H₂ : CO ratio of 1.5 with the fan type reactor and 0.67 with the tubular reactor. In the absence of CO₂, coke is the main carbonaceous product. Under all conditions studied the fan type reactor demonstrated higher methane conversions (up to 11.9%) and selectivities to hydrogen.     

Effect of MgO promoter on Ni-based SBA-15 catalysts for combined steam and carbon dioxide reforming of methane

A series of Ni/SBA-15 catalysts with Ni contents ranging from 5 wt% to 15 wt%, as well as another series of 10%Ni/MgO/SBA-15 catalysts, in which the range of the MgO content was from 1 wt% to 7 wt%, were prepared, and their catalytic performances for the reaction of combined steam and carbon dioxide reforming of methane were investigated in a continuous flow microreactor. The structures of the catalysts were characterized using the XRD, H2-TPR and CO2-TPD techniques. The results indicated that the CO selectivity for this reaction was very close to 100%, and the H2/CO ratio of the product gas could be controlled by changing the H2O/CO2 molar ratio of the feed gas. The simultaneous and plentiful existing of steam and CO2 had a significant influence on the catalytic performance of the 10%Ni/SBA-15 catalyst without modification. After reacting at 850 °C for 120 h over this catalyst, the CH4 conversion dropped from 98% to 85%, and the CO2 conversion decreased from 86% to 53%. However, the 10%Ni/3%MgO/SBA-15 catalyst exhibited a much better catalytic performance, and after reacting for 620 h, the CO2 conversion over this catalyst dropped from 92% to around 77%, while the CH4 conversion was not decreased. Oxidation of the Ni0 species as well as carbon deposition during the reaction were the main reasons for the deactivation of the catalyst without modification. On the other hand, modification by the MgO promoter improved the dispersion of the Ni0 species, and enhanced the CO2 adsorption affinity which in turn depressed the occurring of carbon deposition, and thus retarded the deactivation process.