Mesoporous zirconia-modified clays supported nickel catalysts for CO and CO2 methanation

The Ni catalysts supported on a new structure with zirconia nanoparticles highly dispersed on the partly damaged clay layers has been prepared by the incipient wetness impregnation method and the new structure of the support has been prepared in one pot by the hydrothermal treatment of the mixture of the clay suspension and the ZrO(NO₃)₂ solution. The catalytic performances for the CO and CO₂ methanation on the catalysts have been investigated at a temperature range from 300 °C to 500 °C at atmospheric pressure. The catalysts and supports have been characterized by X-ray diffraction (XRD), transmittance electron microscopy (TEM), H₂ temperature-programmed reduction (H₂-TPR), nitrogen adsorption–desorption, and thermogravimetry and differential thermal analysis (TG-DTA). It is found that the zirconia-modified clays have the typical bimodal pore size distribution. Most of the pores with the sizes smaller than 10 nm are resulted from the zirconia pillared clays and the mesopores with the sizes larger than 10 nm and the macropores with the sizes larger than 50 nm are resulted from the partly damaged clay layers. The bimodal pore structure is beneficial to the dispersion of Ni on the layers of the zirconia-modified clays and the increase in Ni loading. The zirconia nanoparticles are highly dispersed on the partly damaged clay layers. Nickel oxide in cubic phase is the only Ni species that can be detected by XRD. The nickel oxide nanoparticles with the sizes of 12 nanometers or more are well dispersed on the zirconia-modified clay layers, which are observed to be buried in the stack layers of zirconia. The presence of nickel oxide in six different forms could be perceived on the new structure. Five of them except the Ni species that forms the spinel phase with Al in clays can be reduced to the active Ni species for the CO and CO₂ methanation. But the activity of the Ni species is different, which is associated with the chemical environment at which the Ni species is located. The catalyst with the higher zirconia content, which also has the larger specific surface area and pore volume, exhibits the better catalytic performance for the CO or CO₂ methanation. Zirconia in the catalyst is responsible for the dispersion of the Ni species, and it prevents the metallic Ni nanoparticles from sintering during the process of the reaction. In addition, it is also responsible for the reduction of the inactive carbon deposition. The catalyst with 15 wt.% zirconia content has the highest CO conversion of about 100% and the highest methane selectivity of about 93% at 450 °C for CO methanation, and the catalyst with 20% zirconia content has the CO₂ conversion of about 80% and the highest methane selectivity of about 99% for CO₂ methanation at 350 °C. The catalyst with 15 wt.% zirconia possesses promising stability and no distinct deactivation could be perceived after reaction for 40 h. This new catalyst has great potential to be used in the conversion of the blast furnace gas (BFG) and the coke oven gas (COG) to methane.     

Nickel on a macro-mesoporous Al2O3@ZrO2 core/shell nanocomposite as a novel catalyst for CO methanation

A novel nickel catalyst supported on Al₂O₃@ZrO₂ core/shell nanocomposites was prepared by the impregnation method. The core/shell nanocomposites were synthesized by depositing zirconium species on boehmite nanofibres. This contribution aims to study the effects of the pore structure of supports and the zirconia dispersed on the surface of the alumina nanofibres on the CO methanation. The catalysts and supports were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H₂ temperature-programmed reduction (H₂-TPR), nitrogen adsorption–desorption, and thermogravimetry and differential thermal analysis (TG-DTA). The catalytic performance of the catalysts for CO methanation was investigated at a temperature range from 300 °C to 500 °C. The results of the characterization indicate that the metastable tetragonal zirconia could be stably and evenly dispersed on the surface of alumina nanofibres. The interlaced nanorods of the Al₂O₃@ZrO₂ core/shell nanocomposites resulted in a macropore structure and the spaces between the zirconia nanoparticles dispersed on the alumina nanofibres formed most of the mesopores. Zirconia on the surface of the support promoted the dispersion and influenced the reduction states of the nickel species on the support, so it prevented the nickel species from sintering as well as from forming a spinel phase with alumina at high temperatures, and thus reduced the carbon deposition during the reaction. With the increase of the zirconia content in the catalyst, the catalytic performance for the CO methanation was enhanced. The Ni/Al₂O₃@ZrO₂-15 exhibited the highest CO conversion and methane selectivity at 400 °C, but they decreased dramatically above or below 400 °C due to the temperature sensitivity of the catalyst. Ni/Al₂O₃@ZrO₂-30 exhibited a high and constant rate of methane formation between 350 °C and 450 °C. The excellent catalytic performance of this catalyst is attributed to its reasonable pore structure and good dispersion of zirconia on the support. This catalyst has great potential to be further studied for the future industrial use.     

Carbon nanotube supported Pt-Ni catalysts for preferential oxidation of CO in hydrogen-rich gases

A series of carbon nano-tubes supported platinum-nickel catalysts were prepared and used for CO preferential oxidation in H₂-rich streams. The catalysts were characterized by using N₂-adsorption, XRD, HRTEM, H₂-TPD and H₂-TPR techniques. Effects of platinum and nickel loading amount, CO₂ and H₂O in the feed stream on the activity and selectivity over the catalysts were investigated. The results of catalytic performance tests show that the carbon nano-tubes supported Pt-Ni catalysts are very active and highly selective at low temperature for CO preferential oxidation in 1 vol. % CO, 1 vol. %O₂, 50 vol. % H₂ and N₂ gases. Adding 12.5 vol. % of CO₂ into the feed gases has slight negative influence on CO conversion. Adding 15 vol. % of H₂O leads to a little decrease of CO conversion at the temperature range of 100-120 °C, which is proposed to be caused by capillary wetting of water in the micro-pores of carbon nano-tubes. As the reaction temperature is higher, adding water can improve CO conversion. The characterization results indicate that platinum species are in nano-particles uniformly dispersed on the carbon nano-tubes surface. There are two kinds of nickel species, one is interacted with platinum and likely to form Pt-Ni alloy in reduction process, the other is much highly dispersed on carbon nano-tubes and strongly interacted with the supports. The high activity of the catalysts is attributed to the interaction between Pt and Ni with the formation of Pt-Ni alloy.     

Hydrogen and carbon allotrope production through methane cracking over Ni/bimodal porous silica catalyst: Effect of nickel precursor

Nickel-based catalyst is highly active for hydrogen production through methane cracking reaction at moderate reaction temperature. However, Ni catalyst is easily deactivated by carbon encapsulation. In order to solve this problem, this research studies the effect of nickel precursors—nickel acetate (NA), nickel carbonate (NC) and nickel nitrate (NN)—on the activity and stability of nickel/bimodal porous silica (Ni/BPS) catalyst in methane cracking reaction. It was found that these nickel precursor solutions had different pH values, resulting in different interactions between surface silanol groups of BPS supports and Ni. Among these catalysts, Ni(NC)/BPS catalyst exhibited high nickel dispersion and weak interaction between Ni and BPS support; it then gave the highest CH₄ conversion and better stability compared to the other catalysts. In addition, H₂ yield of Ni(NC)/BPS catalyst was 2.90 and 1.40 times higher than those of Ni(NA)/BPS and Ni(NN)/BPS catalysts, respectively. Moreover, carbon nanofibers were grown in Ni(NC)/BPS and Ni(NN)/BPS catalysts, whereas carbon nanotubes were formed on Ni(NA)/BPS catalyst, due to the different nickel particle sizes, dispersions, and Ni—BPS support interactions.     

Hydrogen production via the glycerol steam reforming reaction over nickel supported on alumina and lanthana-alumina catalysts

In the present work, a comparative study of Ni catalysts supported on commercially available alumina and lanthana-alumina carriers was undertaken for the glycerol steam reforming reaction (GSR). The supports and/or catalysts were characterized by PZC, BET, ICP, XRD, NH₃-TPD, CO₂-TPD, TPR and SEM. Carbon deposited on the catalytic surface was characterized by SEM, TPO and Raman. Concerning the Ni/LaAl sample it can be concluded that the presence of lanthana by: (a) facilitating the active species dispersion, (b) strengthening the interactions between nickel species and support, (c) increasing of the basic sites' population and redistributing the acid ones in terms of strength and density, provides a catalyst with improved performance for the GSR reaction, in terms of activity, H₂ production and long term stability. TPO and Raman indicate that the carbon on the Ni/LaAl catalyst was mostly amorphous and was deposited mainly on the support surface. For the Ni/Al catalyst, graphitic carbon was prevalent and likely covered its active sites.     

Combined steam and CO2 reforming of methane over Co–Ce/AC-N catalyst: Effect of preparation methods on catalyst activity and stability

An appropriate preparation method is the essential to improve the catalyst performance. In this study, Co–Ce/AC-N catalysts were fabricated on N-doped activated carbon supports by impregnation, sol-gel, precipitation and mix methods, respectively. It was used to catalyze the combined steam and dry reforming of methane (CSDRM). The effects of different preparation methods on the catalyst performance were investigated by means of N₂ adsorption-desorption, XRD, H₂-TPR, TEM, CO₂-TPD, FTIR and XPS. Compare with the catalysts prepared by other methods, the catalyst prepared by impregnation exhibits a large surface area, high active metal dispersion, and strong metal-support interaction. Meanwhile, it also has strong basic sites and abundant oxygen vacancies. These greatly improve the activity and stability of the catalyst. The conversions of CH₄ and CO₂ at 650 °C were achieved 71.6% and 64.4%, and H₂/CO was retained at 1.5.     

Methanation of CO on Ru/graphitized-carbon catalysts: Effects of the preparation method and the carbon support structure

Two kinds of Ru/C catalysts prepared by two different methods and supported on two graphitized carbons differing in their surface area were studied in CO methanation in the H₂-rich gas. The textural parameters of the support materials were characterized by means of N₂ physisorption. XRPD, XPS, TEM and CO- chemisorption studies indicate that the application of wet impregnation leads to more homogeneous composition of the Ru/carbon system and higher Ru dispersion than dry impregnation for both supports. The activity of the Ru/carbon samples in CO methanation in a H₂-rich gas stream depends on the structure and average size of the active phase crystallites. The combination of wet impregnation and the use of graphitized carbon of appropriate structure in the preparation of the Ru/C catalyst lead to a complete conversion of CO at 240 °C.     

PtRuMo/C catalysts for direct methanol fuel cells: Effect of the pretreatment on the structural characteristics and methanol electrooxidation

The influence of thermal treatment under different environments of PtRuMo/C catalyst has been investigated for CO and methanol electrooxidation in a half cell and in a DMFC single cell. The PtRuMo/C catalysts were synthesized following two step procedure while the thermal treatments consisted of heating at 300 °C in H₂ or He atmosphere for 1 h. Structural characteristics of the electrocatalysts have been studied employing a wide range of instrumental methods, including physicochemical techniques like X-ray diffraction, TEM, TPR, XPS, and electrochemical techniques like single cell studies and Fourier Transform Infrared Spectroscopy adapted to the electrochemical system for in situ studies. These electrocatalysts exhibited good dispersion and small particle size, which increased upon increasing thermal treatment. Moreover, thermal treatment, mainly under H₂ is responsible for the decrease of the lattice parameter and the increase of the spill over effect to Mo sites. These effects were also accompanied by increasing the proportion of the more reduced Ru species in this catalyst. The electrochemical characterization revealed that although all ternary catalysts were more active towards CO and methanol oxidation than the binary catalyst, the catalyst treated with H₂ improves its performance by ca. 15% higher with respect to the ternary catalysts treated either in He treatment or with no treatment. The enhancement in activity is associated with a change in the reaction path, which promotes the direct oxidation of CHO species to CO₂ without the production of the CO poisoning species. The synergistic effect of the three metals seems to be improved and the Mo–Pt and Mo–Ru interaction strengthened.     

Support effects on the properties of Co and Ni catalysts for the hydrogen production from bio-ethanol partial oxidation

Partial oxidation of bio-ethanol over Co- and Ni-based catalysts supported on Al₂O₃, ZnO and AlZn binary mixed oxide was studied in a temperature range between 300 and 600 °C. Substantial difference in catalytic behavior of the materials was related to variation in metal dispersion and to metal-support interaction realized on different supports. Hence, the state of active metallic phase and reducibility of the catalysts were investigated. Among the presented systems, Ni supported on AlZn mixed oxide prepared by sol–gel method afforded the most active catalyst producing a H₂ and CO rich fuel gas. It is proposed that ZnAl₂O₄ spinel phase determines the reaction pathway and Ni promote the hydrogen generation. High hydrogen selectivity of around 90% at complete ethanol conversion was achieved at 600 °C, whereas CO, CO₂ and insignificant amounts of CH₄ were the only carbon-containing products. This high catalytic performance combined with the low cost metals and the supports used in this study makes the materials prepared herein attractive as candidates for hydrogen generation by catalytic partial oxidation of bio-ethanol.     

Effect of acid treatment on the catalytic performance of CuO/Cryptomelane catalyst for CO preferential oxidation in H2-rich streams

The effect of acid treatment on the catalytic performance of CuO/Cryptomelane (CuO/CR) for CO preferential oxidation (CO-PROX) in H₂-rich streams has been investigated. The CR supports are synthesized via the sol-gel approach. The hydrochloric acid or water is used to treat the CR support, and the corresponding CuO/CR catalysts are prepared by an initial wet impregnation method. Compared with the pristine CuO/CR and water-treated CuO/CR_W catalysts, the acid-treated CuO/CR_H exhibits the best catalytic activity with almost 100% of CO conversion at 110 °C, which can be maintained at least 100 h. The characterization results show that acid treatment decreases the K⁺ content in the CuO/CR_H catalyst, which is conducive to the formation of more oxygen vacancies, thereby promoting the reducibility of CuO/CR_H. This is the main reason for the high catalytic activity of the acid-treated CuO/CR_H catalyst. Moreover, the abundant Brönsted acid sites on CuO/CR_H are favorable for the desorption of acidic product CO₂, which also could result in the significant promotion of the catalytic activity for CO-PROX. This study sheds a light on the importance of acid treatment for cryptomelane and provides an efficient catalyst for hydrogen purification.     

Hydrogen production by auto-thermal reforming of ethanol over Ni catalysts supported on ZrO2: Effect of preparation method of ZrO2 support

Zirconia supports were prepared by a sol–gel method (S-ZrO₂) and by a templating sol–gel method (M-ZrO₂). Nickel catalysts supported on zirconia were then prepared by an incipient wetness impregnation method for use in hydrogen production by auto-thermal reforming of ethanol. For comparison, a commercial zirconia (C-ZrO₂) was also employed as a support for nickel catalyst. The effect of preparation method of zirconia on the catalytic property and catalytic performance of supported nickel catalysts (Ni/C-ZrO₂, Ni/S-ZrO₂, and Ni/M-ZrO₂) was investigated. The crystalline and physical property of zirconia supports and the catalytic performance of supported nickel catalysts were strongly affected by the preparation method of zirconia. BET surface area and pore volume were decreased in the order of M-ZrO₂ > S-ZrO₂ > C-ZrO₂. Both M-ZrO₂ and S-ZrO₂ supports showed only tetragonal phase of ZrO₂, while C-ZrO₂ support exhibited tetragonal and monoclinic phases of ZrO₂. Crystalline size of nickel species in the Ni/ZrO₂ catalysts decreased with increasing surface area and pore volume of ZrO₂ supports. All the Ni/ZrO₂ catalysts exhibited 100% conversion of ethanol at 500 °C, while product distributions over the Ni/ZrO₂ catalysts were different depending on the preparation method of zirconia. Among the catalysts tested, the Ni/M-ZrO₂ catalyst showed the best catalytic performance in hydrogen production by auto-thermal reforming of ethanol. Well developed mesopore, high surface area, and pure tetragonal phase of ZrO₂ were responsible for fine nickel dispersion and high catalytic performance of Ni/M-ZrO₂. C–C bond cleavage reaction and methane steam reforming reaction were also accelerated over the Ni/M-ZrO₂ catalyst.     

Preferential oxidation of CO in a H2-rich stream over multi-walled carbon nanotubes confined Ru catalysts

Multi-walled carbon nanotubes (MWNTs) confined Ru catalysts were prepared by a modified procedure using ultrasonication-aided capillarity action to deposit Ru nanoparticles onto MWNTs inner surface. The structure properties of MWNTs supports and Ru catalysts were extensively characterized by XRD, TGA, H₂-TPR, XPS, TEM, FTIR and Raman spectra. The catalytic performance in the preferential oxidation of CO in a H₂-rich stream was examined in detail with respect to the influences of Ru loading, MWNTs diameter, various pretreatment conditions, and the presence of CO₂ and H₂O in the feed stream. In contrast with Ru catalysts supported on MWNTs external surface and other carbon materials, the superior activity was observed for the MWNTs-confined Ru catalyst, which was discussed intensively in terms of the confinement effect of carbon nanotubes. The optimized catalyst of 5 wt.% Ru confined in MWNTs with diameter of 8–15 nm can achieve the complete CO conversion in the wider temperature range and the favorable stability at 80 °C under the simulated reformatted gas mixture, which proves a promising catalyst for preferential CO oxidation in H₂-rich stream.     

Bioethanol/glycerol mixture steam reforming over Pt and PtNi supported on lanthana or ceria doped alumina catalysts

The catalytic activity of Pt and PtNi catalysts supported on γ-Al₂O₃ modified by La and Ce oxides was investigated in the steam reforming of ethanol/glycerol mixtures. In general, all the catalysts fully converted the glycerol at the temperatures tested. However, the conversion of ethanol depended on the reaction temperature and catalyst type. The conversion into gaseous products operating at 500 °C and 450 °C was 100% using the most active catalysts (PtNiAl6La and PtNiAl10Ce). These two bimetallic catalysts gave H₂ yields close to those predicted by thermodynamic equilibrium at these temperatures. However, when the reaction temperature was lowered to 400 °C, these catalytic systems and the PtNiAl one recorded a significant decrease in ethanol conversion and H₂ yield, which moved away from the thermodynamic equilibrium value. This deviation was due to intermediate liquid products (acetaldehyde, acrolein, etc.) not being further reformed and the formation of other gaseous ones (light alkanes and ethylene). PtNiAl10Ce catalyst presented the highest conversion into gas at 400 °C, resulting in the largest H₂ yield, followed by PtNiAl6La and PtNiAl catalysts. This order is in agreement with the Ni/Al surface atomic ratio measured by XPS technique in reduced samples. However, filamentous carbon nanotubes were detected but this carbon type maintained the active sites accessible for reactants, since TEM and TGA results showed that the density of this carbon was lower for PtNiAl₁₀Ce catalyst. Pt catalysts presented lower activity than PtNi catalysts possibly due to the formation of carbon nanotubes, which covered some metallic active sites.     

Anti-sintering mesoporous Ni–Pd bimetallic catalysts for hydrogen production via dry reforming of methane

In this work, a series of mesoporous silica supported nickel or nickel-palladium catalysts were synthesized and performed in dry reforming of methane (DRM) reaction for producing syngas. Compared with the monometallic catalyst, the Ni–Pd bimetallic catalysts, especially synthesized by the OA-assisted route, exhibited promising yields of H₂ and CO in the catalytic DRM reaction, achieved at 63% and 69% over NiPd-SP-OA bimetallic catalyst at the reaction temperature of 700 °C, respectively. TEM image results confirmed that no obvious sintering phenomenon happened on spent NiPd-SP-OA bimetallic catalyst within 1550 min time-on-stream reaction. Based on the results of XRD, XPS and H₂-TPR, it could be known that the superior catalytic performance on NiPd-SP-OA catalyst were main ascribed to the smaller-sized Ni nanoparticles with a uniform metal dispersion and a larger fraction of exposed active sites (Ni⁰).     

Effect of preparation method of mesoporous Ni–Al2O3 catalysts on their catalytic activity for hydrogen production by steam reforming of liquefied natural gas (LNG)

Mesoporous Ni–Al₂O₃ catalysts were prepared by impregnation method (NiAl-IP), co-precipitation method (NiAl-CP), and sequential precipitation method (NiAl-SP) for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of preparation method of mesoporous Ni–Al₂O₃ catalysts on their catalytic activity for steam reforming of LNG was investigated. Physicochemical properties of Ni–Al₂O₃ catalysts were strongly influenced by the preparation method of Ni–Al₂O₃ catalysts. Surface area, pore volume, and average pore size of Ni–Al₂O₃ catalysts decreased in the order of NiAl-SP > NiAl-CP > NiAl-IP. Nickel species strongly interacted with Al₂O₃ supports through the formation of nickel aluminate phase. Surface nickel aluminate phase of Ni–Al₂O₃ catalysts was readily reduced after the reduction process, while bulk nickel aluminate phase of NiAl-CP catalyst was hardly reducible. Nickel dispersion and nickel surface area of Ni–Al₂O₃ catalysts decreased in the order of NiAl-SP > NiAl-CP > NiAl-IP. Among the catalysts tested, NiAl-SP catalyst with the highest nickel surface area showed the best catalytic performance in the steam reforming of LNG. Furthermore, finely dispersed nickel species in the NiAl-SP catalyst efficiently suppressed the carbon deposition during the reaction.     

Controlling the rate of change of Ni dispersion in commercial catalyst by ALD overcoat during dry reforming of methane

This study investigates changes in dispersion with time-on-stream of a Ni catalyst coated with alumina by Atomic Layer Deposition (ALD) in Dry Reforming of Methane (DRM) conditions. A 20 wt% commercial Ni catalyst is coated with 5, 10, and 20 ALD cycles and tested for DRM at 650 °C, 1 atm for 40 h. Using an in-situ H₂–CO pulse chemisorption technique, it is found that the rate of decline in catalyst dispersion is more rapid in the uncoated catalyst (~0.11%h⁻¹) than 5-ALD catalyst (~0.025%h⁻¹). TEM images before and after reaction show that the average particle size for the uncoated catalyst increases from 8.5 nm to 24.5 nm, indicating sintering, whereas the 5-ALD catalyst retained the initial particle size. The reduced particle size also explains the 50% reduction in carbon formation-rate in the 5-ALD catalyst. The developed sequential H₂–CO chemisorption technique reliably measures in-situ dispersion in uncoated and ALD coated catalysts with exposed active sites.     

Methanation over Ni/SiO2: Effect of the catalyst preparation methodologies

We confirmed here that the catalyst preparation methodologies have a significant effect on the activity and stability of Ni/SiO₂ catalyst for methanation of syngas (CO + H₂). Catalyst characterizations using X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and transmission electron microscope (TEM) were performed to investigate the structure and performance of the catalysts. The activity and stability of catalysts prepared by thermal decomposition and dielectric-barrier discharge (DBD) plasma decomposition of nickel precursor were compared. The plasma decomposition results in a high dispersion, an enhanced interaction between Ni and the SiO₂ support, as well as less defect sites on Ni particles. Enhanced resistance to Ni sintering was also observed. In addition, the plasma prepared catalyst effectively inhibits the formation of inactive carbon species. As a result, the plasma prepared catalyst exhibits significantly improved activity with enhanced stability.     

New performing hydroxyapatite-based catalysts in dry-reforming of methane

Dry reforming of methane (DRM) is a promising process for the production of synthetic gas from carbon dioxide and methane. However, the design of a performing catalyst for this reaction is still challenging since catalyst deactivation usually takes place, principally by thermal sintering at high temperatures (700–950 °C) and by carbon deposition. In this work, calcium hydroxyapatite (HAP) and HAP-doped magnesium (Mg_HAP) supported nickel catalysts were synthesized by wet precipitation method, characterized by various physico-chemical and thermal techniques, and evaluated in DRM reaction. Outstanding catalytic performance in DRM could be obtained with Ni/ HAP and Ni/Mg_HAP catalysts, thanks to a tunable acidity-basicity of these supports, a strong metal-support interaction, and a good thermal stability of nickel nanoparticles. H₂ and CO were the main products, with stable selectivity up to 85 ∓ 3%, while H₂O and solid carbon were byproducts with 5–10% of selectivity.     

Methane cracking using Ni supported on porous and non-porous alumina catalysts

Porous and non-porous alumina catalysts were used as nickel supports to catalyze methane cracking. Different operating parameters were studied in a thermal gravimetric analyzer, including methane and hydrogen partial pressures, temperature and flow rate. During CH₄ cracking, carbon builds up on the catalyst surface and therefore the catalyst requires periodic regeneration. Cycling tests were performed, using air during the regeneration phase to burn off the carbon. The results showed that the non-porous catalyst performed better than the porous catalyst in terms of cracking during the first cycle. Full regeneration of the catalysts by oxidizing the deposited carbon was achieved at 550 °C, while oxidation was very slow at 500 °C. After full regeneration, the performance of the porous catalyst became considerably better than the non-porous. The porous catalyst kept its activity for 24 cracking/regeneration cycles, while the non-porous catalyst lost half of its activity by the second cracking cycle and almost all of its activity after six cycles. NiAl₂O₄ formation and Ni sintering caused the non-porous catalyst activity loss. TPO results showed that two carbon types were deposited on the catalysts, namely Cβ and Cγ, where Cβ is more active than Cγ.     

Effects of synthesis methods on performance of CuZn/MCM-41 catalysts in methanol steam reforming

CuZn-based catalysts are active in production of hydrogen by methanol steam reforming. However, there is a need to have further insight on their physico-chemical properties to improve selectivity to hydrogen. Therefore, a series of CuZn/MCM-41 catalysts was synthesized by four different routes; one pot hydrothermal synthesis (OPMCM), co-impregnation (COMCM), serial impregnation (SRMCM) and copper impregnated on Zn-MCM-41 (ZNMCM). Samples of catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), inductively coupled plasma (ICP) emission spectrometry, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). XRD revealed disruption in the ordered pore network typical in MCM-41 for all catalysts synthesized and also showed that the one pot synthesis catalyst had wide spread dispersion of Cu and Zn. SEM micrographs captured irregularly shaped particles of different sizes. While XPS showed that different Cu and Zn species were formed within the catalyst matrix. XPS also confirmed that there was wide spread dispersion and interaction of Cu and Zn with MCM-41 matrix in the OPMCM catalyst. COMCM and OPMCM demonstrated the highest activity with 88 and 65% methanol conversion with corresponding H₂ selectivity of 91 and 86% respectively. They are better than SRMCM and ZNMCM which had average H₂ selectivity of 19% and 31% respectively. CO selectivity was less than 1.8% for the COMCM and OPMCM catalysts. While SRMCM and ZNMCM had CO selectivity's as high as 8.9% and 7.2% respectively. The data generated shows that catalytic activity is largely affected by the nature of Cu species within the catalyst matrix.