Catalysts For CO2 Reforming Research Articles

Enhanced activity and coke resistivity of NiCoFe nanoalloy catalyst in CO2 reforming of methane

NiCo nanoalloy catalysts were prepared from hydrotalcite precursors and used in CO2 reforming of methane (DRM) under atmospheric and 2 MPa pressure in a fixed-bed reactor at 700-850 °C. The Ni6Co1 catalyst with a molar ratio of Ni/Co to 6 showed the highest stability and activity in DRM under atmospheric pressure. This was due to the homogeneous dispersion of nanoalloy particles (∼14 nm) on the MgAl(O) support, which had a strong metal-support interaction. Nonetheless, a slow and continuous deactivation was spotted under 2 MPa pressure due to the coke deposition. Further modification of Ni6Co1 with optimum amount of Fe (in Ni6Co0.5Fe0.5) formed ternary NiCoFe nanoalloy with improved metal-support interaction and reduced alloy size (∼10 nm). The presence of Fe significantly improved the coke resistance capability and provided high stability under 2 MPa pressure.

Effects of synthesis parameters on the activity of cubic OMA supported nickel catalyst in CO2 reforming of methane

Effects of synthesis parameters on the activity of cubic OMA supported nickel catalyst in CO2 reforming of methane

Deactivation and in-situ regeneration of Dy-doped Ni/SiO2 catalyst in CO2 reforming of methanol

The self-regeneration of Ni-based catalysts has been considered as a promising approach to maintain not only a continuous but also economical process. However, the effect of catalyst nature, operating temperature, amount and types of carbon deposits on the effectiveness of the in-situ regeneration is still not well-investigated. Therefore, in this work, the self-regeneration ability of the undoped and Dy-doped Ni/SiO2 catalysts, which were prepared by the same impregnation method, were examined in the dry reforming of methanol. The physicochemical properties of the fresh and spent catalysts were analyzed by various techniques such as X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD), transmission electron microscopy (TEM), N2-BET isothermal adsorption. The nature and chemical reactivity of coke deposits formed during dry reforming at various temperatures (550, 600, and 650 °C) and the regeneration possibility of used catalysts through CO2 gasification at these temperatures were investigated by the in-situ temperature-programmed gasification by CO2 (TPCO2). The Dy additive significantly improves the dispersion of the nickel active sites of Ni/SiO2 catalyst, as demonstrated by the decreased Ni crystal size as well as the increased specific surface area and reduction degree of the catalyst. Furthermore, Dy promotion increases the quantity of oxygen vacancies and the nature of oxygen species, thereby improving the catalyst activity and stability. Specifically, methanol conversion dropped from 93% to 96%–61% and 31% for undoped Ni/SiO2 at 600 °C and 650 °C, respectively and from about 99% to 87% (at 600 °C) and 52% (at 650 °C) for Dy-doped catalyst.

In Situ Fabrication of Ultrasmall Ni Nanoparticles from Ni(OH)2 Precursors for Efficient CO2 Reforming of Methane

Metal size is a critical structural parameter for Ni-based catalysts in CO2 reforming of methane. Herein, ultrasmall Ni nanoparticles (3.7 nm) were fabricated from Ni(OH)2 precursors on γ-Al2O3 nanoplates via a simple solution method followed by H2 reduction. The resultant Ni/Al2O3-IS catalyst showed competitive reforming performance. The turnover frequency reached 15.3 s–1 at 700 °C under atmospheric pressure. Methane (CH4) conversion declined marginally from 79.8 to 70.2% after 20 h of reaction. Characterization results reveal that high activity and good stability were endowed by the ultrasmall Ni size and superior coke resistance, respectively. A bifunctional reaction mechanism was identified on the Ni/Al2O3-IS catalyst, wherein the activation of the reactant molecules was facilitated near metal–support interfaces. This work offers a novel strategy to fabricate ultrasmall Ni particles and provides new insights into structure–activity relationships in CO2 reforming of methane.

Effect of lattice oxygen in Ni-Fe/Bio-char on filamentous coke resistance during CO2 reforming of tar

The catalyst deactivation resulted from filamentous coke deposition limits the application of CO2 reforming technology in solid waste gasification process. The bimetallic Ni-Fe catalysts have excellent encapsulating coke resistance in steam reforming of oxygenates tar, but the filamentous coke resistance of Ni-Fe/Bio-char in CO2 reforming of non-oxygenates tar remains unclear. To investigate the filamentous coke during CO2 reforming process, a non-oxygenates tar, toluene was select as filamentous coke precursor in CO2 reforming experiment. Based on the comparison between Ni/Bio-char and Ni-Fe/Bio-char, the effect of lattice oxygen in on filamentous coke resistance was explored. During CO2 reforming experiment, Ni-Fe/Bio-char showed higher hydrogen conversion (48.90–56.33%) and carbon conversion (53.57–62.94%) than Ni/Bio-char. Besides, the iron sites in the Ni-Fe oxide can be converted to iron oxide under CO2 atmosphere, providing more lattice oxygen to oxidize the filamentous coke deposition on catalysts surface. However, the lattice oxygen in Ni-Fe/Bio-char was rapidly consumed by the oxidation of massive filamentous coke, resulting in 21% of filamentous coke still accumulated on Ni-Fe/Bio-char. Overall, in addition to the oxidation capacity of filamentous coke, the inhibition ability to filamentous coke formation is critical to the filamentous coke resistance of catalyst in CO2 reforming of tar. The obtained results can provide a reference for the design of catalyst applied in CO2 reforming.

CO2 reforming of methane over activated carbon-Ni/MgO-Al2O3 composite catalysts for syngas production

The composite catalysts AC-Ni/MgO-Al2O3 were prepared by the co-precipitation method with activated carbon (AC) and [Ni,Mg,Al]-hydrotalcite as the precursors, and characterized by XRD, TG-DTG, N2 adsorption, H2-TPR and SEM, respectively. The resultant catalysts were examined for CO2 reforming of methane. The results showed that the introduction of AC into Ni/MgO-Al2O3 catalyst improved the textural properties, especially the surface area and pore volume of mesopores, and decreased the size of metal Ni. Compared with Ni/MgO-Al2O3, the composite AC-Ni/MgO-Al2O3 exhibited higher catalytic activity, stability and H2/CO ratio. But the AC content obviously influenced the catalytic performances. High AC loading resulted in the decline of catalytic activity owing to lower surface area and fewer active Ni content in the catalyst. 10AC-Ni/MgO-Al2O3 with 10% AC displayed the best catalytic activity and stability compared with Ni/MgO-Al2O3. About 86.2% conversion of CH4, 91.3% conversion of CO2 and above 0.95 ratio of H2/CO were achieved over 10AC-Ni/MgO-Al2O3 sample for the reaction time of 5430 min. This work provides a route to improve catalytic performances of Ni-based catalysts in CO2 reforming of methane.

Effect of Preparation Technique on the Performance of Ni and Ce Incorporated Modified Alumina Catalysts in CO2 Reforming of Methane

Performances of modified sol–gel alumina (MSGA) based catalysts, synthesized in an inert atmosphere and activated by Ni and Ce were investigated in CO2 reforming of methane. Two different incorporation methods were used to dope Ce into the structure of the catalysts: (i) simultaneous impregnation of Ce together with Ni (Ni–Ce@MSGA), (ii) one-pot synthesis of Ce incorporated alumina support material (Ni@Ce-MSGA). In the second case Ni was impregnated on the Ce-MSGA support. Synthesized catalysts were characterized using TPR, XRD, N2 adsorption/desorption, pyridine adsorbed DRIFT, CO2-TPD techniques. These analyses showed that the synthesized catalysts possessed reduced Ni particles, as well as mesoporous structure, Lewis acid sites and moderate basicity. The modified sol–gel alumina and modified sol–gel Ce-MSGA supported catalysts showed stable activity in CO2 reforming of methane. Ce incorporation improved catalytic activity of the synthesized catalysts and reduced the occurrence of reverse water gas shift reaction. Ni–Ce@MSGA catalyst decreased the CO2/CH4 conversion ratio much higher than Ni@Ce-MSGA catalyst. Coke analysis were determined using TGA/DTA, XRD, and SEM analysis. Especially, simultaneous impregnation of Ce and Ni catalyst inhibited coke deposition significantly due to lattice oxygen of ceria. However, coke deposition over Ni@Ce-MSGA catalyst was higher than Ni@MSGA catalyst since Ni@Ce-MSGA catalyst has higher nickel crystal size than that of Ni@MSGA catalyst.

A highly active Ni catalyst supported on Mg-substituted LaAlO3 for carbon dioxide reforming of methane

The pristine and Mg-substituted LaAlO3 perovskites were synthesized by the citrate sol-gel method and employed as supports for Ni catalysts in CO2 reforming of methane. The Mg/La molar ratio of 2/8 was determined as the optimal amount of Mg substitution in Ni/La1-xMgxAlO3-δ catalysts. Compared with the Ni/LaAlO3 catalyst, the Ni/La0.8Mg0.2AlO2.9 catalyst exhibited enhanced initial activity and improved stability. Structural characterizations including N2 sorption (N2 sorption), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX) elemental mapping, thermogravimetry-differential scanning calorimetry (TG-DSC), CO2 temperature-programmed desorption (CO2-TPD), X-ray photoelectron spectroscopy (XPS) and H2 temperature-programmed reduction (H2-TPR) were performed to elucidate the effect of Mg partial substitution. It is revealed that much smaller Ni nanoparticles were formed with Mg partial substitution, which may explain the enhanced reforming activity. The improved stability over the Ni/La0.8Mg0.2AlO2.9 catalyst was rationalized with better anti-coke and anti-sintering properties, which was closely related with surface basicity, oxygen vacancies and metal-support interactions. The present work demonstrates that perovskites with appropriate surface modification can serve as novel supports for the preparation of highly active catalysts.

Effects of the Mg addition on characteristics and catalytic activity of Ni/-Al2O3 in dry reforming of methane

Effectively using CO2-containing natural gas is an urgent requirement in Vietnam. Therefore, producing hydrogen and syngas by dry reforming of methane (СН4+СО2 = 2Н2+2СО) has gained renewed interest in recent years. In this paper, Ni/α- Al2O3 and Ni-Mg/α-Al2O3 catalysts were prepared by impregnation. Physico-chemical characteristics of catalysts were investigated via nitrogen physisorption (BET), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and Temperature Programmed Reduction (TPR) methods. The activities of catalysts in CO2 reforming of CH4 were studied in a micro-flow reactor in the temperature range 550 –800oC, and content of CH4 and CO2 of 3 % mol. It was found that the conversion of CH4 and CO2 remarkably increased with the increase of reaction temperature from 550 to 700oC, but increased inconsiderably when the temperature reached more than 700oC. The selectivities of CO and H2 reached over 91 %. The modification of Ni/α- Al2O3 catalyst with Mg led to reduce the NiO particle size forme the new ZnO-MgO solid solution and increase the reductivity of catalyst. These improve the activity, selectivity and stability of catalyst. At the reaction temperature of 700oC, the conversions of CH4 and CO2 on Ni-Mg/α-Al2O3 reached 88.5 % and 72.3 %, respectively. The activities of catalysts were stable for 30 hours of reaction. Moreover, the role of Mg in the resistance to the coke formation on the catalyst surface was clarified via the results of temperature programmed oxidation (TPO) of spent catalysts after running the reaction for 30 hours at 700oC

Promotional effect of Mg in trimetallic nickel-manganese-magnesium nanocrystalline catalysts in CO2 reforming of methane

In the present paper, the dry reforming reaction was studied over the 10 wt%Ni-3wt.%Mn-x wt.% Mg (x = 2, 4 and 6 wt%) catalysts supported on γ-Al2O3 with mesoporous structure. The physicochemical characteristics of the samples were determined by XRD, BET, TPO, and SEM techniques. Mesoporous γ-Al2O3 carrier with the high BET area (186 m2/g) was synthesized by a simple sol–gel method and the Ni, NiMn and Mg promoted catalysts possessed nanocrystalline mesoporous structure with the BET area in the range of 127–176 m2/g. The average pore radius of the prepared catalysts were smaller than 11 nm. All the synthesized samples exhibited a CH4 conversion in the range of 60–65% at 700 °C. The small differences in methane conversion in all catalysts could be related to the same nickel loading. According to the TPR results, the Mg addition caused an increase in the reducibility of the nickel catalyst and the Mg-promoted sample exhibited a higher conversion compared to the monometallic catalyst, due to its higher reducibility. The results showed that the textural characteristics of the catalysts were affected by the content of Mg. The results indicated that the NiMn/Al2O3 catalyst promoted by 4 wt% Mg showed the highest CH4 conversion in all studied reaction temperatures (550–700 °C). Furthermore, only one oxidation peak was detected for all catalysts in TPO analysis, which was related to the filamentous form carbon. The 10Ni/Al2O3 and 10Ni3Mn4Mg/Al2O3 catalysts exhibited the highest and the lowest amount of deposited filamentous carbon, respectively. The 10Ni3Mn4Mg/Al2O3 catalyst was stable during the 20 h time on stream without any decline in CH4 conversion.

CO2 reforming of methane to syngas at high pressure over bi-component Ni-Co catalyst: The anti-carbon deposition and stability of catalyst

The catalytic performance of Ni-Co bi-component catalysts in CO2 reforming of methane (CRM) under high pressures was studied for obtaining highly stable Ni-based catalysts, which is important for the industrialization of high pressure CRM. A series of 5% (xNiyCo)/SBA-15 catalysts were prepared with a modified co-impregnation method by adding trace amount of β-cyclodextrin (CD) into Ni(NO3)2 impregnation solution. The effects of catalyst compositions (Ni/Co ratio) and the CRM reaction conditions (pressure, gas hourly space velocity, time on stream, etc) on the catalysts stabilities were investigated. The carbon deposition behaviors of the catalysts during the high pressure CRM reaction were disclosed through detailed characterizations of the spent catalysts. The type of coke, instead of the amount of deposited carbon, was proved to be responsible for the deactivation of 5% (xNiyCo)/SBA-15 catalysts during the high pressure reaction. The amount of carbon deposition depended strongly on the Co loading in the bimetallic catalysts. Long-term stability with 100 h TOS at 2.0 MPa and 800 °C was achieved for the optimized 5% (4.5Ni0.5Co)/SBA-15 catalyst and a slow deactivation (decrease in CH4 conversion) was observed. The reaction results with different reaction time over 5% (4.5Ni0.5Co)/SBA-15 at high pressures suggested that the accumulation of carbon deposition took place mainly at the initial stage of the CRM reaction. Moreover, the disorder degree of deposited carbon species and the sintering of metal particles were identified as the primary reasons for the deactivation of the catalysts. Trace Co enriched on Ni-Co surface of 5% (4.5Ni0.5Co)/SBA-15 suppressed Ni aggregation and facilitated the adsorption of co-reactant.

Ni/MgO[sbnd]Al2O3 catalyst derived from modified [Ni,Mg,Al]-LDH with NaOH for CO2 reforming of methane

[Ni,Mg,Al]-layered double hydroxide (LDH) was modified with NaOH solution to prepare the LDH-derived Ni/MgOAl2O3 catalyst and characterized by X-ray diffraction, inductively coupled plasma optical emission spectrometer, scanning electron microscope, transmission electron microscopy, temperature programmed desorption of CO2 or NH3, N2 adsorption, and thermogravimetry analysis, respectively. The resultant Ni/MgOAl2O3 catalysts were used for CO2 reforming of CH4. The results showed that the concentration of NaOH solution has an obvious effect on the structure of LDH and catalytic performances of the resultant nickel-based catalysts. Aluminum species in LDH was partly dissolved with increasing NaOH solution concentration, resulting in the increase of [M2+/M3+] molar ratio and the interlayer spacing of modified LDHs. The surface area and pore volume, especially mesoporous surface area and pore volume, were improved compared with parent [Ni,Mg,Al]-LDH, and the catalytic activity of the resultant Ni/MgOAl2O3 catalyst in CO2 reforming of CH4 was enhanced. NaOH concentration has a slight influence on CO2 conversion and stability of the resultant Ni/MgOAl2O3 catalyst. The Ni/MgOAl2O3 prepared from the modified [Ni,Mg,Al]-LDH with 0.1 mol/L NaOH exhibits the best stability and anti-coke deposit ability. CH4 and CO2 conversions retain at about 91% and 96%, respectively, along with a H2/CO ratio of about 0.90 after reaction of 28 h. High CO2/CH4 molar ratio can improve catalytic stability, resistance to coke deposit and Ni sintering of the catalyst.

Development of Flexible Catalyst Material for Internal Dry Reforming

Direct internal reforming solid oxide fuel cell (DIRSOFC) fueled by biogas has been investigating with the motivation of downsizing and cost reduction of SOFC systems. While chemical energy of biogas composed of CH4 and CO2 can be directly converted to electricity without an external fuel reformer, this direct conversion can cause carbon deposition within Ni-stabilized zirconia cermet anode, hence SOFC performance degrades rapidly [1,2]. To solve this issue, paper-structured catalyst (PSC), flexible catalyst made up of inorganic fibre (Cf) network in which metallic catalysts for fuel reforming such as Ni, Ru, etc. are dispersed, is now being studied [3,4]. In this work, three types of Ni-loaded PSCs were prepared via the simple paper making process [3,4]. Fig. 1 shows the SEM images of Ni-loaded PSCs, (a) without the dispersion of support oxide particles in the fibre network (Ni-PSC), (b) with the dispersion of (Mg,Al)O derived from hydrotalcite (Ni/(Mg,Al)O-PSC) and (c) with the dispersion of (Ce,Zr)O2 (Ni/(Ce,Zr)O2-PSC). In the case of Ni-PSC, because Ni particles are loaded on the smooth surface of amorphous Cf, Ni coarsening was significantly promoted resulting in Ni particle size of 200-500 nm. On the other hand, when the oxide particles are dispersed in the fibre network, fine Ni particles < 10 nm were formed on the oxide particles to have higher contact area with gaseous reactants and prevent Ni particles from agglomeration at high operation temperature. The results of the tests of CH4 dry reforming (CH4 + CO2 → 2H2 + 2CO) carried out at 750 oC with GHSV of 3500 h-1 are shown in Fig. 2. Compared to Ni-PSC and Ni/(Mg,Al)O-PSC, Ni/(Ce,Zr)O2-PSC exhibited higher CH4 conversion close to 90 %. Moreover after the 15 h test, carbon deposition was not observed inside of the Ni/(Ce,Zr)O2-PSC, whereas formation of whisker carbon was noticeable for the Ni/(Mg,Al)O-PSC. This indicates that lattice oxygen in the (Ce,Zr)O2 contributed to oxidization of carbonaceous species deposited on the catalyst surface to regenerate active sites for dry reforming reaction. Now, the performances of SOFC with and without PSCs are being evaluated in the direct feed of simulated biogas mixture at 750 oC. Keywords: Paper-structured catalyst, ceria, internal reforming, biogas, dry reforming. Reference: [1] Wang S., Lu G. Effects of promoters on catalytic activity and carbon deposition of Ni/γ-Al2O3 catalyst in CO2 reforming of CH4. J. Chem. Technol. Biotechnol. (2000), 75, 589-595. [2] Ke K., Gunji A., Mori H., Tsuchida S., Takahashi H., Ukai K et al. Effect of oxide on carbon deposition behaviour of CH4fuel on Ni/ScSZ cermet anode in high temperature SOFCs. Solid state ionics (2006), 177, 541-541. [3] Shiratori Y., Sakamoto M. Performance improvement of direct internal reforming solid oxide fuel cell fuelled by H2S-contaminated biogas with paper-structured catalyst technology. Journal of Power Sources (2016), 332, 170-179. [4] Shiratori Y., Q. T. Tran, Sasaki. K. Performance enhancement of biodiesel fueled SOFC using paper-structured catalyst. Int. J. Hydrogen Energy (2013), 38 (23), 9856-9866. Figure 1

Syngas Production from CO2 Reforming and CO2-steam Reforming of Methane over Ni/Ce-SBA-15 Catalyst

This study compares the catalytic performance of mesoporous 10 Ni/Ce-SBA-15 catalyst for CO2 reforming and CO2-steam reforming of methane reactions in syngas production. The catalytic performance of 10 Ni/Ce-SBA-15 catalyst for CO2 reforming and CO2-steam reforming of methane was evaluated in a temperature-controlled tubular fixed-bed reactor at stoichiometric feed composition, 1023 K and atmospheric pressure for 12 h on-stream with gas hourly space velocity (GHSV) of 36 L gcat-1 h-1. The 10 Ni/Ce-SBA-15 catalyst possessed a high specific BET surface area and average pore volume of 595.04 m2 g-1. The XRD measurement revealed the presence of NiO phase with crystallite dimension of about 13.60 nm whilst H2-TPR result indicates that NiO phase was completely reduced to metallic Ni0 phase at temperature beyond 800 K and the reduction temperature relied on different degrees of metal-support interaction associated with the location and size of NiO particles. The catalytic reactivity was significantly enhanced with increasing H2O/CO2 feed ratio. Interestingly, the H2/CO ratio for CO2-steam reforming of methane varied between 1 and 3 indicated the occurrence of parallel reactions, i.e., CH4 steam reforming giving a H2/CO of 3 whilst reverse water-gas shift (RWGS) reaction consuming H2 to produce CO gaseous product.

NiO–MgO Solid Solution Prepared by Sol–Gel Method as Precursor for Ni/MgO Methane Dry Reforming Catalyst: Effect of Calcination Temperature on Catalytic Performance

The influence of calcination temperature (500, 600 and 700 °C) on NiO–MgO solid solution formation and the performance of the resulting catalysts in CO2 reforming of methane was studied. The solid solutions and resulting catalysts were characterized by Brunauer–Emmett–Teller, XRD, temperature-programmed reduction (TPR), TEM and thermal gravimetric analysis techniques. Catalytic performance tests were carried out under 550–750 °C, 1 bar, CO2/CH4 = 1–3 mol/mol and space velocities of 30,000–120,000 ml/(h gcat). The catalyst calcined at 600 °C exhibited the best performance in terms of catalytic activity and stability and showed lowest amount of coke formation after 50 h-on-stream. The effect of calcination temperature on degree of NiO–MgO solid solution formation was demonstrated by both XRD and TPR profiles. The 600 °C calcination temperature was found to be an optimum as it caused modest NiO–MgO interaction, which is responsible for complete formation of the NiO–MgO solid solution with high nickel dispersion and resistant to coke formation.

Effects of Nd, Ce, and La modification on catalytic performance of Ni/SBA-15 catalyst in CO2 reforming of CH4

Rare-earth metal (Nd, Ce, and La) oxides modified Ni/SBA-15 catalysts were prepared by a β-cyclodextrin-modified impregnation method. The physicochemical properties of the catalysts were characterized using X-ray diffraction, N2 adsorption-desorption, temperature-programmed reduction, and thermogravimetric analysis. The catalytic performance of the catalysts was evaluated in the CO2 reforming of CH4 to syngas. The characterization results showed that Nd, Ce, and La modification had little effect on the textural structures and crystalline phases of the obtained catalysts but influenced the reduction of NiO species. Addition of Nd favored interactions between Ni and SiO2, possibly as a result of the formation of Ni-Nd-O species. The results for the CO2 reforming of CH4 revealed that the addition of suitable amounts of Nd (5–10 wt%) improved the catalytic activity and stability. A small amount of carbon was deposited over the used Nd-modified catalysts. The properties of Ni/SBA-15 catalysts modified with La and Ce were similar to those of the Nd-modified catalysts.

Redox dynamics of Ni catalysts in CO2 reforming of methane

The influence of redox dynamics of a Ni/MgAl oxide catalyst for dry reforming of methane (DRM) at high temperature was studied to correlate structural stability with catalytic activity and coking propensity. Structural aging of the catalyst was simulated by repeated temperature-programmed reduction/oxidation (TPR/TPO) cycles. Despite a very high Ni loading of 55.4wt.%, small Ni nanoparticles of 11nm were obtained from a hydrotalcite-like precursor with a homogeneous distribution. Redox cycling gradually changed the interaction of the active Ni phase with the oxide support resulting in a crystalline Ni/MgAl2O4-type catalyst. After cycling the average particle size increased from 11 to 21nm – while still a large fraction of small particles was present – bringing about a decrease in Ni surface area of 72%. Interestingly, the redox dynamics and its strong structural and chemical consequences were found to have only a moderate influence on the activity in DRM at 900°C, but lead to a stable attenuation of carbon formation due to a lower fraction of graphitic carbon after DRM in a fixed-bed reactor. Supplementary DRM experiments in a thermobalance revealed that coke formation as a continuous process until a carbon limit is reached and confirmed a higher coking rate for the cycled catalyst.

Effects of Yb2O3 promotor on the performance of Ni/SiC catalysts in CO2 reforming of CH4

Ni/SiC and Ni-Ybx/SiC (x=2%, 4%, 6%, 10%) catalysts were prepared by the impregnation method, and the performances of catalysts in the carbon dioxide reforming of methane were studied in a fixed-bed reactor. The catalysts were characterized by BET, ICP-AES, XRD, H2-TPR, TG-DTA, XPS and TEM techniques. The experimental results indicate that the appropriate addition amount of Yb is 4% to 6%. Ni-Yb4/SiC and Ni-Yb6/SiC catalysts exhibit excellent catalytic activity and stability at 800°C, and the conversion of CH4 and CO2 can be maintained over 90% during the 100 h testing. Yb2O3 promotor can inhibit the growth of nickel nanoparticles and reduce the amount of carbon deposition, therefore Ni-Yb/SiC catalysts show stable activity in the continuous reforming reaction.

Effects of support modifiers on the catalytic performance of Ni/Al2O3 catalyst in CO2 reforming of methane

The effect of alkaline earth metals (MgO, CaO and BaO) on activity, stability and coke formation of Ni/Al2O3 catalysts in CO2 reforming of methane (CRM) was investigated. These catalysts were prepared with impregnation method and characterized by XRD, BET, TPR, TPO and SEM techniques and tested in CO2 reforming of methane. The results showed that addition of these support modifiers to the Ni/Al2O3 catalysts decreased the surface area of catalysts (SBET) but improved the activity and stability and reduced the coke formation due to increasing the basicity of the supports. In addition, among these modifiers, MgO had the greatest impact on catalytic activity and coke formation process. Meanwhile, Ni/MgO–Al2O3 catalyst with various Mg contents were prepared, characterized with BET, TPR, TPO and SEM techniques and studied in CRM. It was found that just a moderate amount of Mg could improve catalytic stability and decreased coke formation in CRM.

Study of stability of Ni/MgO/γ-Al2O3 catalyst prepared by plasma for CO2 reforming of CH4

The Ni-based catalyst with MgO promoter was prepared by atmospheric pressure cold plasma, and it showed excellent catalytic activity and stability compared with other two correlative reference catalysts in CO2 reforming of CH4 under the conditions of 1atm, 800°C, gas hourly space velocity (GHSV)=30L/(hg), n(CH4)/n(CO2)=4/6. The XRD, TEM and XPS results proved that the good performance benefited from the combined effect of plasma reduction and MgO addition. The plasma reduction endued the catalyst with smaller primal Ni crystals by its atomic hydrogen effect at the relatively low temperature (740K) and short time (10min), and this effect can prevent the growth of Ni crystals during the reduction process; MgO promoter made for “freezing” Ni crystals by the interaction between MgO and Ni, and this interaction can not only suppress the agglomeration of Ni crystals during the reaction process, but also mitigate the decomposition of CH4 and improve the activation of CO2 as a result of the enhanced basicity of the catalyst.