Impact of Sr Addition on Zirconia-Alumina-Supported Ni Catalyst for COx-Free CH4 Production via CO2 Methanation.

Zirconia-alumina-supported Ni (5Ni/10ZrO2+Al2O3) and Sr-promoted 5Ni/10ZrO2+Al2O3 are prepared, tested for carbon dioxide (CO2) methanation at 400 °C, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, surface area and porosity, infrared spectroscopy, and temperature-programmed reduction/desorption techniques. The CO2 methanation is found to depend on the dispersion of Nickel (Ni) sites as well as the extent of stabilization of CO2-interacted species. The Ni active sites are mainly derived from the reduction of 'moderately interacted NiO species'. The dispersion of Ni over 1 wt % Sr-promoted 5Ni/10ZrO2+Al2O3 is 1.38 times that of the unpromoted catalyst, and it attains 72.5% CO2 conversion (against 65% over the unpromoted catalyst). However, increasing strontium (Sr) loading to 2 wt % does not affect the Ni dispersion much, but the concentration of strong basic sites is increased, which achieves 80.6% CO2 conversion. The 5Ni4Sr/10ZrO2+Al2O3 catalyst has the highest density of strong basic sites and the highest concentration of active sites with maximum Ni dispersion. This catalyst displays exceptional performance and achieves approximately 80% CO2 conversion and 70% methane (CH4) yield for up to 25 h on steam. The unique acidic-basic profiles composed of strong basic and moderate acid sites facilitate the sequential hydrogenation of formate species in the COx-free CH4 route.

Hydrogen Production via Methane Decomposition over Alumina Doped with Titanium Oxide-Supported Iron Catalyst for Various Calcination Temperatures.

The decomposition of methane has been chosen as an alternative method for producing hydrogen. In this study, 20 % Fe was used as the active metal part of the catalyst. To better comprehend the impact of the supporting catalytic properties, alumina and titania-alumina composite were investigated as supports. Iron-based catalysts were prepared by impregnation method and then calcined at different temperatures (300 °C, 500 °C, and 800 °C). The catalysts were examined at 800 °C under atmospheric pressure with a 15 mL/min total flow rate and 2 : 1 CH4 to N2 feed ratio. The textural and morphological characteristics of the fresh calcined and spent catalysts were investigated. The catalytic activity and stability data demonstrated that Fe supported over TiO2-Al2O3 calcined at 500 °C performed the best of all evaluated catalysts with a more than 80 % hydrogen yield. The Raman spectra result showed that graphitic carbon was produced for all used titanium dioxide catalysts. Moreover, according to transmission electron microscopy (TEM) results, the carbon deposited on the catalysts' surface is carbon nanotubes (CNT).

Alumina-Magnesia-Supported Ni for Hydrogen Production via the Dry Reforming of Methane: A Cost-Effective Catalyst System.

5Ni/MgO and 5Ni/γAl2O3 are pronounced in the line of cheap catalyst systems for the dry reforming of methane. However, the lower reducibility of 5Ni/MgO and the significant coke deposition over 5Ni/γAl2O3 limit their applicability as potential DRM catalysts. The mixing capacity of MgO and Al2O3 may overcome these limitations without increasing the catalyst cost. Herein, a 5Ni/xMg(100 - x)Al (x = 0, 20, 30, 60, 70, and 100 wt. %) catalyst system is prepared, investigated, and characterized with X-ray diffraction, surface area and porosity measurements, H2-temperature programmed reduction, UV-Vis-IR spectroscopy, Raman spectroscopy, thermogravimetry, and transmission electron microscopy. Upon the addition of 20 wt. % MgO into the Al2O3 support, 5Ni/20Mg80Al is expanded and carries both stable Ni sites (derived through the reduction of NiAl2O4) and a variety of CO2-interacting species. CH4 decomposition at Ni sites and the potential oxidation of carbon deposits by CO2-interacting species over 5Ni/20Mg80Al results in a higher 61% H2-yield (against ~55% H2-yield over 5Ni/γAl2O3) with an excellent carbon-resistant property. In the major magnesia support system, the 5Ni/60Mg40Al catalyst carries stable Ni sites derived from MgNiO2 and "strongly interacted NiO-species". The H2-yield over the 5Ni/60Mg40Al catalyst moves to 71%, even against a high coke deposition, indicating fine tuning between the carbon formation and diffusion rates. Ni dispersed over magnesia-alumina with weight ratios of 7/3 and 3/7 exhibit good resistance to coke. Weight ratios of 2/8 and 7/3 contain an adequate amount of reducible and CO2-interactive species responsible for producing over 60% of H2-yield. Weight ratio 6/4 has a proper coke diffusion mechanism in addition to achieving a maximum of 71% H2-yield.

Understanding Coke Deposition Vis-à-Vis DRM Activity over Magnesia-Alumina Supported Ni-Fe, Ni-Co, Ni-Ce, and Ni-Sr Catalysts.

The catalytic conversion of CH4 and CO2 into H2-rich syngas is known as the dry reforming of methane (DRM). The dissociation of CH4 over active sites, coupled with the oxidation or polymerization of CH4-x (x = 1-4), plays a crucial role in determining in determining the DRM product yield and coke deposition. Herein, a series of bimetallic-supported catalysts are prepared by the dispersion of Ni-M (M = Ce, Co, Fe, and Sr) over 60 wt% MgO-40 wt% Al2O3 (60Mg40Al) support. Catalysts are tested for DRM and characterized with XRD, surface area and porosity, temperature-programmed reduction/desorption, UV-VIS-Raman spectroscopy, and thermogravimetry. 2.5Ni2.5Sr/60Mg40Al and 2.5Ni2.5Fe/60Mg40Al, and 2.5Ni2.5Ce/60Mg40Al and 2.5Ni2.5Co/60Mg40Al have similar CO2 interaction profiles. The 2.5Ni2.5Sr/60Mg40Al catalyst nurtures inert-type coke, whereas 2.5Ni2.5Fe/60Mg40Al accelerates the deposition of huge coke, which results in catalytic inferiority. The higher activity over 2.5Ni2.5Ce/60Mg40Al is due to the instant lattice oxygen-endowing capacity for oxidizing coke. Retaining a high DRM activity (54% H2-yield) up to 24 h even against a huge coke deposition (weight loss 46%) over 2.5Ni2.5Co/60Mg40Al is due to the timely diffusion of coke far from the active sites or the mounting of active sites over the carbon nanotube.

Methane Decomposition to Hydrogen Over Zirconia-Supported Fe Catalysts-Effects of the Modified Support.

Methane decomposition is a promising route to synthesize COx -free hydrogen and carbon nanomaterials (CNMs ). In this work, the impregnation method was employed for the preparation of the catalysts. Systematic investigations on the activity and stability of Fe-based catalysts were carried out in a packed-bed micro-activity reactor at 800 °C with a feed gas flow rate of 18 mL/min. The effect of doping Y2 O3 , MgO, SiO2 and TiO2 over ZrO2 on the catalytic performance was also studied. BET revealed that the specific surface areas and pore volumes are increased after SiO2 , TiO2 , and Y2 O3 are added to ZrO2 while MgO had a negative impact and hence a little decrease in specific surface area is observed. The catalytic activity results showed that the Fe-based catalyst supported over TiO2 -doped ZrO2 that is, Fe-TiZr, demonstrated the highest activity and stability, with a maximum methane conversion of 81.3 % during 180 min time-on-stream. At 800 °C, a maximum initial methane conversion of 73 %, 38 %, 64 %, and 69 % and a final carbon yield of 121 wt. %, 55 wt. %, 354 wt. %, and 174 wt. % was achieved using Fe-MgZr, Fe-SiZr, Fe-TiZr and Fe-YZr catalysts, respectively. Moreover, bulk deposition of uniform carbon nanotubes with a high degree of graphitization and different diameters was observed over the catalysts.

Hydrogen Production from Gadolinium-Promoted Yttrium-Zirconium-Supported Ni Catalysts through Dry Methane Reforming.

Hydrogen production from dry reforming of methane (DRM) not only concerns with green energy but also involves the consumption of two greenhouse gases CH4 and CO2. The lattice oxygen endowing capacity, thermostability, and efficient anchoring of Ni has brought the attention of the DRM community over the yttria-zirconia-supported Ni system (Ni/Y + Zr). Herein, Gd-promoted Ni/Y + Zr is characterized and investigated for hydrogen production through DRM. The H2-TPR → CO2-TPD → H2-TPR cyclic experiment indicates that most of the catalytic active site (Ni) remains present during the DRM reaction over all catalyst systems. Upon Y addition, the tetragonal zirconia-yttrium oxide phase stabilizes the support. Gadolinium promotional addition up to 4 wt % modifies the surface by formation of the cubic zirconium gadolinium oxide phase, limits the size of NiO, and makes reducible NiO moderately interacted species available over the catalyst surface and resists coke deposition. The 5Ni4Gd/Y + Zr catalyst shows about ∼80% yield of hydrogen constantly up to 24 h at 800 °C.

Effect of Adding Gadolinium Oxide Promoter on Nickel Catalyst over Yttrium-Zirconium Oxide Support for Dry Reforming of Methane.

The dry reforming of methane (DRM) was studied for seven hours at 800 °C and 42 L/(g·h) gas hourly space velocity over Ni-based catalysts, promoted with various amounts of gadolinium oxide (x = 0.0, 1.0, 2.0, 3.0, 4.0, and 5.0 wt.%) and supported on mesoporous yttrium-zirconium oxide (YZr). The best catalyst was found to have 4.0 wt.% of gadolinium, which resulted in ∼80% and ∼86% conversions of CH4 and CO2, respectively, and a mole ratio of ∼0.90 H2/CO. The addition of Gd2O3 shifted the diffraction peaks of the support to higher angles, indicating the incorporation of the promoter into the unit cell of the YZr support. The Gd2O3 promoter improved the catalyst basicity and the interaction of NiO with support, which were reflected in the coke resistance (6.0 wt.% carbon deposit on 5Ni+4Gd/YZr; 19.0 wt.% carbon deposit on 5Ni/YZr) and the stability of our catalysts. The Gd2O3 is believed to react with carbon dioxide to form oxycarbonate species and helps to gasify the surface of the catalysts. In addition, the Gd2O3 enhanced the activation of CH4 and its conversion on the metallic nickel sites.

Effect of Holmium Oxide Loading on Nickel Catalyst Supported on Yttria-Stabilized Zirconia in Methane Dry Reforming.

The carbon dioxide reforming of methane has attracted attention from researchers owing to its possibility of both mitigating the hazards of reactants and producing useful chemical intermediates. In this framework, the activity of the nickel-based catalysts, supported by yttria-stabilized zirconia and promoted with holmium oxide (Ho2O3), was assessed in carbon dioxide reforming of methane at 800 °C. The catalysts were characterized by N2-physisorption, H2 temperature-programmed reduction, temperature-programmed desorption of CO2, X-ray diffraction, scanning electron microscopy (SEM) together with energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) techniques. The effect of holmium oxide weight percent loading (0.0, 1.0, 2.0, 3,0, 4.0, and 5.0 wt %) was examined owing to its impact on the developed catalysts. The optimum loading of Ho2O3 was found to be 4.0 wt %, where the methane and carbon dioxide conversions were 85 and 91%, respectively. The nitrogen adsorption-desorption isotherms specified the mesoporous aspect of the catalysts, while the SEM images displayed a morphology of agglomerated, porous particles. The TEM images of the spent catalyst displayed the formation of multiwalled carbon nanotubes. TGA of the 4.0 wt % of Ho2O3 catalyst, experimented over 7-hour time-on-stream, displayed little weight loss (<14.0 wt %) owing to carbon formation, indicating the good resistance of the catalyst to carbon accumulation due to the enhancing ability of Ho2O3 and its adjustment of the support.

Modification of CeNi0.9Zr0.1O3 Perovskite Catalyst by Partially Substituting Yttrium with Zirconia in Dry Reforming of Methane.

Methane Dry Reforming is one of the means of producing syngas. CeNi0.9Zr0.1O3 catalyst and its modification with yttrium were investigated for CO2 reforming of methane. The experiment was performed at 800 °C to examine the effect of yttrium loading on catalyst activity, stability, and H2/CO ratio. The catalyst activity increased with an increase in yttrium loading with CeNi0.9Zr0.01Y0.09O3 catalyst demonstrating the best activity with CH4 conversion >85% and CO2 conversion >90% while the stability increased with increases in zirconium loading. The specific surface area of samples ranged from 1−9 m2/g with a pore size of 12−29 nm. The samples all showed type IV isotherms. The XRD peaks confirmed the formation of a monoclinic phase of zirconium and the well-crystallized structure of the perovskite catalyst. The Temperature Program Reduction analysis (TPR) showed a peak at low-temperature region for the yttrium doped catalyst while the un-modified perovskite catalyst (CeNi0.9Zr0.1O3) showed a slight shift to a moderate temperature region in the TPR profile. The Thermogravimetric analysis (TGA) curve showed a weight loss step in the range of 500−700 °C, with CeNi0.9Zr0.1O3 having the least carbon with a weight loss of 20%.

Hydrogen production from CO2 reforming of methane using zirconia supported nickel catalyst.

The use of hydrogen as an alternative fuel is an attractive and promising technology as it contributes to the reduction of environmentally harmful gases. Finding environmentally friendly cheap active metal-based catalysts for H2 rich syngas via dry reforming of methane (DRM) for industrial applications has posed a challenge. In this paper, H2 production via CO2 reforming of methane was investigated over 5Ni/ZrO2 catalysts. The catalytic performance of all prepared catalysts was evaluated in a microtubular fixed bed reactor under similar reaction conditions (i.e., activation temperature at 700 °C, feed flow rate of 70 ml min-1, reaction temperature 700 °C for 440 min reaction time) of CO2 reforming of methane. Different characterization techniques such as; BET, CO2-TPD, TGA, XRPD, Raman, and TEM, were used. The study of the textural properties of catalysts established that the BET of pristine catalyst (5NiZr) was enhanced by the addition of modifiers and promoters. A bimodal TPR distribution in the reduction temperature range of 250-550 °C was recorded. In the CO2-TPD analysis, the strength of basicity came in this order: 5Ni15YZr > 5Ni10YZr > 5Ni5YZr > 5NiZr > 5Ni20YZr. The investigation of catalyst modifiers (MgO and Y2O3) resulted in the Y2O3 modifier improving the activity and catalytic performance better than MgO, which generated a hydrogen yield of 22%. 15% Y2O3 modifier loading gave the highest H2 yield 53% in the phase of different loadings of yttria. The study of the influence of promoters (Cs, Ga, and Sr) revealed that the catalytic performance of 5Ni15YZr catalysts promoted with Sr towards the H2 yield enhanced the activity to 62%. The promoted catalysts displayed lower carbon deposition compared to the unpromoted catalyst, which provided 25.6 wt% weight loss.

Yttria Modified ZrO2 Supported Ni Catalysts for CO2 Reforming of Methane: The Role of Ce Promoter.

Yttria modified zirconia (YZ) supported on 5 wt % of Ni-based catalysts promoted with ceria (1-3 wt %) were prepared by the impregnation process to investigate their performance for dry reforming of methane. The reforming reactions, conducted at 700 °C and at atmospheric pressure using a CO2/CH4/N2 fixed feed ratio of 3/3/1, with a total flow rate of 70 mL/min, revealed that the ceria-promoted catalysts (xCe-Ni-YZ; x = 1-3 wt %) enhanced the CH4 and CO2 conversions as compared to the reference catalyst (Ni-YZ). A CO2 conversion of 85% was exhibited by the 3Ce-Ni-YZ catalyst. Despite increased conversions, xCe-Ni-YZ catalysts showed more amounts of carbon deposition as evidenced by the values of TGA, and hence were found to be less stable as compared to the reference Ni-YZ catalyst. The used and fresh catalysts were characterized by BET, H2-TPR, XRD, TEM, Raman, TPD, and TGA. TEM images displayed nanoparticle sizes of Ni in the fresh catalysts, while carbon filaments were formed on the spent catalysts. The CO2-TPD, H2-TPR, and BET results revealed the existence of only weak and moderate basic sites, the increase of total hydrogen consumption, and the surface area values with the addition of the Ce promoter, respectively. The TGA analysis showed that the Ce promoter increased the carbon deposition, while the Raman results indicated the dominance of crystallinity due to the graphitized carbon.

Study of Partial Oxidation of Methane by Ni/Al2O3 Catalyst: Effect of Support Oxides of Mg, Mo, Ti and Y as Promoters.

Catalysts of 10% Ni, supported on promoted alumina, were used to accomplish the partial oxidation of methane. The alumina support was doped with oxides of Mo, Mg, Ti and Y. An incipient wetness impregnation technique was used to synthesize the catalysts. The physicochemical properties of the catalysts were described by XRD, H2-TPR (temperature programmed reduction), BET, TGA, CO2-TPD (temperature-programmed desorption) and Raman. The characterization results denoted that Ni has a strong interaction with the support. The TGA investigation of spent catalysts displayed the anticoking enhancement of the promoters. The impact of the support promoters on the catalyst stability, methane conversion and H2 yield was inspected. Stability tests were done for 460 min. The H2 yields were 76 and 60% and the CH4 conversions were 67 and 92%, respectively, over Ni/Al2O3+Mg, when the reaction temperatures were 550 and 650 °C, respectively. The performance of the present work was compared to relevant findings in the literature.

Promotional effect of magnesium oxide for a stable nickel-based catalyst in dry reforming of methane.

The generation of synthesis gas (hydrogen and carbon monoxide mixture) from two global warming gases of carbon dioxide and methane via dry reforming is environmentally crucial and for the chemical industry as well. Herein, magnesium-promoted NiO supported on mesoporous zirconia, 5Ni/xMg-ZrO2 (x = 0, 3, 5, 7 wt%) were prepared by wet impregnation method and then were tested for syngas production via dry reforming of methane. The reaction temperature at 800 °C was found more catalytically active than that at 700 °C due to the endothermic feature of reaction which promotes efficient CH4 catalytic decomposition over Ni and Ni-Zr interface as confirmed by CH4-TSPR experiment. NiO-MgO solid solution interacted with ZrO2 support was found crucial and the reason for high CH4 and CO2 conversions. The highest catalyst stability of the 5Ni/3Mg-ZrO2 catalyst was explained by the ability of CO2 to partially oxidize the carbon deposit over the surface of the catalyst. A mole ratio of hydrogen to carbon monoxide near unity (H2/CO ~ 1) was obtained over 5Ni/ZrO2 and 5Ni/5Mg-ZrO2, implying the important role of basic sites. Our approach opens doors for designing cheap and stable dry reforming catalysts from two potent greenhouse gases which could be of great interest for many industrial applications, including syngas production and other value-added chemicals.

Methane Decomposition Over ZrO2-Supported Fe and Fe-Ni Catalysts-Effects of Doping La2O3 and WO3.

A leading method for hydrogen production that is free of carbon oxides is catalytic methane decomposition. In this research, Fe and Fe-Ni supported catalysts prepared by the wet impregnation method were used in methane decomposition. The effects of doping the parent support (ZrO2) with La2O3 and WO3 were studied. It was discovered that the support doped with La2O3 gave the best performance in terms of CH4 conversion, H2 yield, and stability at the test condition, 800°C and 4,000-ml h-1 g-1 cat. space velocity. The addition of Ni significantly improved the performance of all the monometallic catalysts. The catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), temperature-programmed reduction/oxidation (TPR/TPO), thermogravimetric analyzer (TGA), and microscopy (SEM and Raman) techniques. Phases of the different forms of Fe were identified by XRD. BET showed a drastic decline in the specific surface area of the catalysts with respect to the supports. TPR profiles revealed a progressive change in the valency of Fe in its combined form to the zero valence-free metal. The La2O3-promoted support gave the best performance and maintained good stability during the time on stream.

Silica-immobilized ionic liquid Brønsted acids as highly effective heterogeneous catalysts for the isomerization of n-heptane and n-octane.

Metal-free imidazolium-based ionic liquid (IL) Brønsted acids 1-methyl imidazolium hydrogen sulphate [HMIM]HSO4 and 1-methyl benzimidazolium hydrogen sulphate [HMBIM]HSO4 were synthesized. Their physicochemical properties were investigated using spectroscopic and thermal techniques, including UV-Vis, FT-IR, 1H NMR, 13C-NMR, mass spectrometry, and TGA. The ILs were immobilized on mesoporous silica gel and characterized by FT-IR spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller analysis, ammonia temperature-programmed desorption, and thermogravimetric analysis. [HMIM]HSO4@silica and [HMBIM]HSO4@silica have been successfully applied as promising replacements for conventional catalysts for alkane isomerization reactions at room temperature. Isomerization of n-heptane and n-octane was achieved with both catalysts. In addition to promoting the isomerization of n-heptane and n-octane (a quintessential reaction for petroleum refineries), these immobilized catalysts are non-hazardous and save energy.