SYNGAS PRODUCTION BY DRY REFORMING OF METHANE OVER CO- PRECIPITATED CATALYSTS

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1 International Journal of Advanced Research in Engineering and Technology (IJARET) Volume 6, Issue 11, Nov 2015, pp , Article ID: IJARET_06_11_001 Available online at ISSN Print: and ISSN Online: IAEME Publication SYNGAS PRODUCTION BY DRY REFORMING OF METHANE OVER CO- PRECIPITATED CATALYSTS Sanjay P. Gandhi and Sanjay S. Patel Institute of Technology, Nirma University, Ahmadabad, Gujarat, India ABSTRACT The syngas manufacturing from the reforming of methane with carbon dioxide is tempting because of output in terms of extra pure synthesis gas and lower H 2 to CO ratio than other synthesis gas production methods like either partial oxidation or steam reforming. For production of long-chain hydrocarbons though the Fischer-Tropsch synthesis, lower H 2 to CO ratio is required and important, as it is a most likely feedstock. In recent decades, CO 2 utilization has become more and more important in view of the emergent global warming phenomenon. On the environmental point of view, methane reforming is tantalizing due to the reduction of carbon dioxide and methane emissions as both are consider as dangerous greenhouse gases. Commercially, as cost effectively, nickel is used for methane reforming reactions due to its availability and lower cost compared to noble metals. Number of catalysts endures rigorous deactivation because of carbon deposition. Mainly carbon formation is because of methane decomposition and CO disproportionate. It is important and required to recognize essential steps of activation and conversion of CH 4 and CO 2 to design catalysts that minimize deactivation. Effect of promoters on activity and stability were studied in the detail. In order to develop the highly active with minimum coke formation the alkali metal oxides and ceria/zirconia/magnesia promoters were incorporated in the catalysts. The influence of ZrO 2, CeO 2 and MgO, in the performance of Ni-Al 2 O 3 catalyst, prepare by co-precipitation method was studied in detailed. The XRD, FTIR, and BET and reactivity test for different promoted and unprompted catalyst was carried out. Key words: CH 4 /CO 2 reforming, percentage of Ni loading, Coke formation, FTIR. Cite this Article: Sanjay P. Gandhi and Sanjay S. Patel. Syngas Production by Dry Reforming of Methane over Co-Precipitated Catalysts. International 1 editor@iaeme.com

2 Sanjay P. Gandhi and Sanjay S. Patel Journal of Advanced Research in Engineering and Technology, 6(11), 2015, pp INTRODUCTION Utilization of CO 2, via a reaction with CH 4 to produce a mixture of CO and H 2 known as synthesis gas and process is called as dry reforming of methane (DRM) [1]. DRM reaction requires high temperature as reactions are extremely endothermic. The DRM process provides several advantages over steam reforming of methane and out of which the most important one is the production of syngas with a low H 2 /CO ratio, is suitable for use in forming higher levels alcohols. Typical application is production of methanol and fischer-tropsch synthesis H 2 /CO is required around 1, that can be produced by DRM [2, 3]. DRM is also impact on environmental front, as methane and carbon dioxide are greenhouse gases. Feedstock s like biogas, coal bed methane, and natural gas with high CO 2 and CH 4 and are good candidates for dry reforming of methane. CO 2 reforming of methane is an interesting route for converting natural gas into synthesis gas, which can produce clean fuels and other chemicals. The increase in the known reserves of natural gas and the feasibility of exploring natural reserves in remote locations several kilometers from coast and in small fields stimulate the development of gas to liquids technology. Reaction 1 is main reaction out of number of reactions of DRM. The reverse water gas shift reaction (RWGS(2)), the Boudouard reaction (3), and the methane decomposition reaction (4) are side reactions in reforming: In DRM reaction, there is RWGS reaction (2), in which production of CO form consumption of CO 2 and H 2. Because of RWGS reaction the overall CO 2 conversion greater than CH 4. Carbon deposition via boudouard reaction (3) and methane decomposition (4) can deactivate the catalyst are major problems in catalytic CO 2 reforming. Noble metal catalysts have good resistance against coke formation, but their high price and limited availability prevent their practical application [2-4]. Thermodynamic experiments have confirmed the inevitable occurrence of carbon formation over a wide range of catalysts, especially Ni-based ones. On the other hand, higher conversion attained at high temperatures results in sintering of Ni particles. In dry reforming of methane nickel based catalyst have been widely used, However, reaction suffers from low catalytic activity and instability against coke deposition due to the boudouard reaction and the methane decomposition reaction [1]. Even though Ni 2 editor@iaeme.com

3 Syngas Production by Dry Reforming of Methane over Co-Precipitated Catalysts based catalyst are first in choice for the CO 2 reforming due to its activity and reasonable price [4, 5]. Basically, support selection is important, as control of the Nisupport interactions can improve Ni-catalyst activities in CO 2 reforming. High mechanical strength, high surface area, and the low price of alumina make it a suitable for Ni-based catalyst. A wide range of basic promoters, such as La 2 O 3, MgO, CaO, SiO 2 have been investigated to develop more stable supports [1]. The catalyst supports and its preparation methods can influence the activity of catalyst. The present work investigates activity of promoted and un-promoted catalyst prepared by coprecipitation for DRM reaction. 2. EXPERIMENTAL 2.1. Catalyst Preparation Co-precipitation method was used to prepare nickel catalyst promoted with ziroconia, cerioum and magnesia. Required amount of nickel nitrate, zirconyl nitrate, cerium nitrate, magnesium nitrate, aluminum nitrate, dissolved in distilled water separately as per stoichiometric quantities. The solution were prepared separately and then mixed in a volume proportion corresponding to the final composition of the catalysts to be obtained. The resulting solution was stirred and heated in a beaker. The aqueous 1M Na 2 CO 3 solution was added drop-wise to the nitrate solution under vigorous stirring until ph 10 was attained at 333 K temperature. The precipitation was allowed to age for 1 h at room temperature with stirring. The excess solution was removed by filtration. The precipitate was washed by double distilled water at a room temperature followed by several times by double distilled water at room temperature in order to remove the sodium salts. The drying was carried out at 373 K for overnight. This material was the catalyst precursor, which was crushed to fine powder and subsequently the catalyst was produced by calcinations in the presence of air at 873 K for 4 hr [1,3]. Analytic grade nickel nitrate, aluminum nitrate, cerium nitrate, zirconyl nitrate were used as a catalyst precursor, support and promoter in the reforming reaction Catalyst activity The CO 2 reforming of methane was carried out at K and atmospheric pressure, using 1 gm catalyst in a stainless steel tubular fixed-bed reactor. Fixed bed reactor having tube of mm inner, mm outer diameter and tube length 500 mm. Activation of the Ni-Catalyst involved reductive treatment with hydrogen at 773 K for 2 h with heating rate of 10 deg per min. The reactant feed gas was passed in composition of CH 4 :CO 2 :N 2 1:1:1 with total flow rate of 500 ml/min having GHSV of cm 3 /g*h. The exit gases were analysed with gas chromatography equipped with thermal conductivity detector with Porapak Q and a SA molecular sieve column was used [7]. In this work, conversions of methane and carbon dioxide and yields of hydrogen and carbon monoxide were calculated according to the following formulas. X CH4 % = [C CH4in -C CH4out ]/ C CH4in * 100 X CO2 % = [C CO2in -C CO2out ]/ C CO2in * 100 Y H2 % = C H2out /2C CH4in *100 Y CO % = C COout /[C CH4in +C CO2in ] * editor@iaeme.com

4 Sanjay P. Gandhi and Sanjay S. Patel Where Xi and Yi are the conversion of reactants and yields of products, respectively Ci in is the initial molar fraction of component i in the feed, and Ci out is the final molar fraction of component i in the product stream [10]. 3. CATALYST CHARACTERIZATION 3.1. XRD The X-ray diffraction (XRD) patterns are studied in order to monitor not only the catalyst structure but also the studied for the identification of the crystalline phase, Model: X PERT MPD, Make: Philips, Holland was used. Information on crystallographic structure, chemical composition and physical properties of materials and then films; x-ray scattering technique is used. XRD is a part of non destructive analytical techniques [10]. These techniques are based on observing the scattered intensity of on x-ray beam hitting a sample as a function of incident and scattered angle, Polarization and wavelength or energy [12] Physisorption Analysis For determining the surface area and pore size distribution of solids, measurement of gas adsorption isotherms are widely used. The identification types of isotherm are required for interpretation of physisorption isotherm. This in turn allows for the possibility to choose an appropriate procedure for evaluation of the textural properties. Non-specific Brunauer-Emmett-Teller (BET) method is the most commonly used standard procedure to measure surface areas, in spite of the over simplification of the model on which the theory is based. The BET equation is applicable at low p/po range and it is written in the linear form: [11] Sample pressure is p, Saturation vapour pressure is p o, The amount of gas adsorbed at the relative pressure p/p o, : n a The monolayer capacity, and C is the so-called BET constant: n a m The adsorption-desorption data to be use for to assess the micro-and mesoporosity and to compute pore size distribution, through number of way has been developed. These are number of assumptions, e.g. relating to pore shape and mechanism of pore filling for same Fourier Transforms Infrared Spectroscopy (FTIR) FTIR spectroscopy gives information on interaction of absorbed molecules, yielding information on [4, 5] 1) The site of interaction, i.e the active centers, 2) The restriction of molecular motion in the adsorbed state. 3) The geometry of the sorption complex and 4) The change of internal bonding due to adsorption. To obtain an infrared spectrum of absorption, emission, photoconductivity or raman scattering of a solid, liquid or gas fourier transform infrared spectroscopy is a 4 editor@iaeme.com

5 Syngas Production by Dry Reforming of Methane over Co-Precipitated Catalysts technique used. Over a wide spectral range FTIR spectrometer simultaneously collects high spectral resolution data. This confers a significant advantage over a dispersive spectrometer which measures intensity over a narrow range of wavelengths at a time [5]. 4. RESULTS AND DISCUSSION 4.1. X-Ray Diffraction of 5%Ni/5%CeO 2 -Al 2 O 3 and 10%Ni/5%MgO- Al 2 O 3 The XRD patterns for Al 2 O 3 supported, prepared by co-precipitation, 5%Ni, and with different promoters (CeO 2 and MgO) are shown in Fig. 1 and 2. The Al 2 O 3, Ni, NiO, CeO 2, MgO, NiAl 2 O 4 and MgAl 2 O 4 phases were detected in the XRD patterns. By increase of nickel loading the ratio of NiO intensity to Al 2 O 3 intensity was improved. In fresh catalyst the spectra corresponding to Ni was observed even at low Ni loading. Second, peak depends on other situation like (a) most probable case of low Nickel loading on the catalyst or (b) Formation of the NiAl 2 O 4 phase [9]. According to the JCPDS files, the Al 2 O 3, Ni, NiO, CeO 2, MgO, NiAl 2 O 4 and MgAl 2 O 4 phases can be detected in the XRD patterns [15]. NiO diffraction peaks observed at , 43.4, 44.5, 62.9, 63.0, 75.6 and Characteristic diffraction peaks of phases at 2 of 19.2, 31.6, 45.3, 56.4, 60.0, 66.2 and 2 of 19.1, 31.4, 37, 45, 59.7, and 65.5 are assigning to MgAl 2 O 4 and NiAl 2 O 4 respectively [7-9]. The smaller amount of Ni interact with alumina and form nickel aluminate (NiAl 2 O 4 ) composite layer, which is an amorphous phase or a crystalline phase with crystallite sizes smaller than the detection limit of XRD. Basically a crystallite size of NiAl 2 O 4 is smaller than the recognition limit of XRD. Figure 1 X-Ray diffraction pattern of the catalyst 10%Ni/5%CeO 2 -Al 2 O 3 In Fig. 1, the XRD patterns of 10Ni/5%CeO 2 -Al 2 O 3 shows intense diffraction lines of NiO (2θ= 43.2 ), Al 2 O 3 (2θ = 66.3 ) and CeO 2 (2θ = 29, 57 ). In this catalyst single major phases of alumina and crystalline phase of nickel and two of phases of CeO 2 were detected. The amount of CeO 2 addition influenced the intensities of 5 editor@iaeme.com

6 Sanjay P. Gandhi and Sanjay S. Patel Nickel peaks. The weaker and broader the Ni Peak due to the more CeO 2 loading on catalyst. It indicates that addition of CeO 2 effects the nickel dispersion on catalyst. Figure 2 X-Ray diffraction pattern of the catalyst 10%Ni/5%MgO-Al 2 O 3 The overlap of alumina and nickel oxide form composite layer of NiO-Al 2 O 3 which is an amorphous phase. The smaller amount of Ni particle interacts with alumina and form nickel aluminate (NiAl 2 O 4 ). It is clear that strong interaction of nickel metal and alumina lattice to make spinel type solid solution of NiAl 2 O 4. There is NiAl 2 O 4 ; the strong interaction is due to the calcination. The presence of Ni in the form of NiO can be observed in XRD patterns as well. The NiO crystallites are small and well dispersed in catalysts samples as the related peak are quire broad. It should be mentioned that NiO crystals are slightly bigger in the presence of CeO 2 and in contrary, alumina peaks lost their intensity after introduction of CeO 2. According to XRD patterns, big crystal of CeO 2 was observed. In Fig. 2, the XRD patterns of 10%Ni/5%MgO-Al 2 O 3 shows intense diffraction lines of NiO (2θ= 62.7 ), Al 2 O 3 (2θ = 42.8 ) and MgO (2θ = 74.8, 78.7 ). As Ni 2+, Mg 2+, Al 3+, fall in to the same lattice, the formation of solid solution of spinel type of MgAl 2 O 4 and NiAl 2 O 4 is favored under high temperature calcination. As Ni 2+, Mg 2+, Al 3+, fall in to the same lattice, the formation of solid solution of spinel type of MgAl 2 O 4 and NiAl 2 O 4 is favored under high temperature calcination BET Surface Area The surface area, pore size and pore volume of the catalysts containing 5%, 10% Ni by weight and promoted with CeO 2 are presented in table 1. Catalyst Table 1 Physical properties of catalysts. BET Surface Area (m 2 /g) Pore Volume (cm 3 /g) Pore Diameter (nm) 5%Ni/Al2O %Ni/Al2O %Ni/5%CeO2-Al2O editor@iaeme.com

7 Syngas Production by Dry Reforming of Methane over Co-Precipitated Catalysts It appears that catalyst surface area decrease with increased nickel loading from 5% to 10%. As more metal is precipitated, more of the pores originally present are being filled up, this effectively reducing surface area FTIR Analysis FTIR analysis is shown in Fig. 3 and 4. For a more precise IR characterization, spectra were reported in a wide range of frequency cm -1. Figure 3 FTIR Spectra of 10%Ni/CeO 2 -Al 2 O 3. Figure 4 FTIR Spectra of 10%Ni/ZrO 2 -Al 2 O 3. The IR spectra in all cases, exhibit metal-oxygen stretching frequencies in the range cm -1 associated with the vibration of M-O, Al-O and M-O-Al bonds (M=Ni, CeO 2, and ZrO 2 ). Peaks of stretching vibration of structured O-H at 3450 cm -1, and stretching vibration at 1640 cm -1 is due to the physically adsorbed water and clear form the spectrum of the catalysts. 7 editor@iaeme.com

8 Sanjay P. Gandhi and Sanjay S. Patel The residual nitrate compounds present in the catalyst after heat treatment and especially nitrogen used for the reaction is responsible for the appearance of N-O and N-C peaks at 1525 cm -1. The peaks at 415 cm -1 corresponds to the metal-oxygen metal band. This band can also be related to the stretching vibration absorption spectrum of Ni. Absorption peaks of metal oxides (NiO, ZrO 2, and CeO 2 ) arising from inter atomic vibrations are below 1000 cm -1. An absorption peaks at 1400, 1649 and 3450 cm -1 are related to adsorbed water for all materials [14, 17]. Effect of Ni loadings with different promoters at different temperatures In Fig. 05 & 06 shows the Ni loading on the activity of Ni/Al 2 O 3 catalyst presented in terms of feed conversion and product yields in Fig. 05, 06 and 07. Figure 5 CH 4 conversion (%) over different temperature (K) in Dry Reforming of methane. As Ni loading increased up to 10% conversion of both CH 4 and CO 2 were considerably increased. At low Ni-loading conversion of CH 4 and CO 2 were observed low, due to the small active nickel metal and the formation of NiAl 2 O 4 even though their surface area is relatively high compared to 10%Ni loading. When Zirconia added, both CH 4 and CO 2 conversions were strongly increased. It is proposed that the presence of ZrO 2 inhibits the NiAl 2 O 4 formation. Further the Al 2 O 3 surface is changed due to ZrO 2 and Ni is not placed straight onto the Al 2 O 3 but near to ZrO2, as a result CO 2 dissociation increase. Similar results and explanations were also found by Seo et al. [42], explaining that ZrO 2 inhibits the inclusion of nickel species into the lattice of Al 2 O 3, preventing the growth of metallic nickel particles during the reaction step. 8 editor@iaeme.com

9 Syngas Production by Dry Reforming of Methane over Co-Precipitated Catalysts Figure 6 CO 2 conversion (%) over different temperature (K) in Dry Reforming of methane. Figure 7 H 2 /CO Ratio over different temperature (K) in Dry Reforming of methane. This causes gasification of the dissociated oxygen and unsaturated intermediates and promotes the formation of carbon deposit precursors, prevents coke formation in the system [5, 10]. Among all catalyst prepared by co-precipitation, the catalytic activity of 10Ni/5%ZrO 2 -Al 2 O 3 was high. Pompeo et al. also [11] explained the coke reduction capability of ZrO 2 similar to our results. It is also noticeable that CeO 2 promoted catalyst has superior CH 4 conversion then unsupported at all temperature. There are two main causes for same (1) CeO 2 has higher surface basicity compare to alumina and the formation of different types of carbonate like species due to interaction of CeO 2 with CO 2. [18] (2) CeO 2 has oxidative properties and a good capacity for oxygen storage reaction [12]. With effect of CeO 2 ; carbon generated from CH 4 dissociation and on catalyst; carbon atom reacted with oxygencontaining species from the dissociation. Due to the faster reaction rate of carbon 9 editor@iaeme.com

10 Sanjay P. Gandhi and Sanjay S. Patel species formed on Ni/CeO 2 -Al 2 O 3 catalyst, these system exhibits higher activity than Ni/Al 2 O 3 catalyst. The converge of Ni metal by CeOx species induced by strong metal surface interaction and the dispersive ability of CeO 2 preventing the formation of large metal ensembles reduced the carbon deposition on Ni/ CeO 2 -Al 2 O 3. It is worth noting that, excellent performance of MgO in raising of basic sites concentrations and consequently, promoting the adsorption rate of acidic CO 2 [13]. In presence of MgO, there is formation of MgAl 2 O 4 phase and surface rearrangement lead to improvement in catalytic activity [14]. Xu et al [43]. reported that NiO-MgO-Al 2 O 3 catalyst was displaying high catalytic activity and long catalytic stability. Monica Garcia-Dieguze et al [44]. expressed that the Mg incorporation to Ni/Al 2 O 3 catalysts improves the Ni dispersion by surface rearrangement and further reduces the carbon formation. The magnesium aluminate support has been used for steam reforming of hydrocarbons due to its having high sintering resistance ability. It is prominent support for nickel catalysts, as due to its high sintering resistance ability and low acidity stability [15]. Helvio Silvester A. Sousa et al [45]. reported that better catalytic performance was found in case of Nicontaining MgAl 2 O 4 and NiAl 2 O 4 phase due to the increased resistance against physical degradation, but coking was found to decrease activity Effect of temperature For all co-precipitated catalyst the consequence of temperature on the conversion of reactant and product gas (H 2 and CO) yields are given in Fig. 05 to 07. DRM is highly endothermic reaction as temperature increased conversion of CH 4 and CO 2 is increased and also the yields of H 2 and CO [21]. Over all the catalyst and all examined temperatures, the conversions of CO 2 were higher than those of CH 4 which can be due to the existence of RWGS (reaction 2) reaction. Highest 76.55% and 80.13% conversion of CH 4 and CO 2 achieved at 1073 K respectively with 10%Ni loading with effect of ZrO 2. The RWGS is also contributed to higher CO 2 conversion then CH 4 conversion at low temperature, as reported [17]. CH 4 dissociation is also increased and greatly enhanced at higher temperatures. It leads to formation of coke, as conversion of methane is increased. In sort at higher temperature the CH 4 dissociation is a strongly favoured reaction. The increase of CH 4 dissociation is demonstrated not only in terms of feed conversion but also the coke yield. This suggests that the CH 4 decomposition dominates the CO 2 disproportionation for the coke formation at high temperatures, as was thermodynamically calculated by S. Therdhianwong et al [18]. Increase in H 2 /CO ratio was detected when temperature raised, though in all cases ratio was below unity, it indicates that RWGS was always taking place but in lower extent when the temperature increased. Further, most of Ni crystallites remain and partially form NiO with oxygen species dissociated form CO 2 at higher temperature Effect of GHSV Results in Fig. 8 & 9 show the influence of space velocity on catalytic activity for the reaction conversion and H 2 /CO ratio. The space velocity is varied by changing the total flow rate maintains at molar feed ratio of one and catalyst amount of 1 g. Moreover, the CH 4 and CO 2 reforming reaction were conducted at constant temperature of 1073 K. By increasing GHSV form to cm 3 /g*h both CH 4 and CO 2 conversion decrease. As the space velocity increase, yields of H 2 and CO decrease editor@iaeme.com

11 Syngas Production by Dry Reforming of Methane over Co-Precipitated Catalysts For DRM reaction low velocity is suitable for better conversion and product yield. For reaction it is required to interaction between reactant and active Ni particles inside the catalyst pores, in case of high GHSV, the residence time is limiting factor for reaction. In such situation number of reactant remain un-reacted. Number of technical theory was made for above interpretation. At higher GHSV there is external diffusion resistance that lead reduction in both CH 4 and CO 2 conversion, similar to observation of Mark and Maier [20]. According to our results, an increase in GHSV has converse outcome for CH 4 and CO 2 conversion over all sample catalysts high GHSV means lead to a lesser amount of contact time, so reactant does not have sufficient time to penetrate in catalyst pores. In other word, limitation is mass transport at higher GHSV. As shown in Fig. 9 the H 2 and CO yields decreases as GHSV increases for all catalyst. Figure 8 CH 4 (%) and CO 2 (%) conversion over different GHSV (cm 3 /g*h). Figure 9 H 2 /CO ratio over different GHSV cm 3 /g*h 11 editor@iaeme.com

12 Sanjay P. Gandhi and Sanjay S. Patel 4.7. Stability test Improvement and development of low cost catalyst with high activity alongside excellent stability can be properties of a commercial catalyst for DRM. Fig. 10 & 11 gives the methane and carbon dioxide conversion at different time on stream over the three promoted catalysts prepared by co-precipitated method. All of the coprecipitated catalyst samples illustrated the reasonable stability and acceptable performance during reaction time. There is deactivation in all three catalysts upto certain extent. The stability improvement can be anticipated by the ratios between the CH 4 and CO 2 conversion after 12 h (720 min) of time on stream (C12=C1) ratios were 0.78, 0.73, 0.74 for 10Ni%/5%CeO 2 -Al 2 O 3, 10Ni%/5%ZrO 2 -Al 2 O 3 and 10Ni%/5%MgO-Al 2 O 3 respectively. Figure 10 Comparison of stability test of different catalyst over time (h) in terms of CH 4 conversion (%) Figure 11 Comparison of stability test of different catalyst over time (h) in terms of CO 2 conversion (%) 12 editor@iaeme.com

13 Syngas Production by Dry Reforming of Methane over Co-Precipitated Catalysts The stability was better over the CeO 2 promoted catalyst compared to other promoted catalysts. It was clear from results that good stability of the 10%Ni/CeO 2 - Al 2 O 3 catalyst compared to ZrO 2 and MgO promoted catalyst. ZrO 2 and MgO promoted catalysts indicate reducing trend in conversion of reactant and product yield. The rate of the atomic carbon gasification by CO 2 is limited than the rate of atomic carbon formation, and carbon will be polymerized [1, 21], is the major reason for deactivation and it lead to coke formation. If deposited carbon having filamentous structure then it s does not deactivate the nickel sites. In reaction performance, reactant accessible to active metals carried on the top, and as a result the activity remains constant. These polymerized carbon atoms can deactivate Ni particle via two ways: (a) encapsulating carbon or diffusing through the Ni after dissolving and (b) detaching Ni particles from the support. In order to authenticate of this witnessing a look over the mechanism of DRM might be useful. It is indicated that the CH 4 decomposition occurs on the surface of the active metals while CO 2 adsorption take place on the support. Adsorbed CO 2 reacts with carbon species derived from dissociative adsorption of CH 4. Therefore, CO releases and deposited carbon removes. As a result of smaller particle size and enhanced dispersion, higher surface area obtained and subsequently the rate of the carbon removal promotes. It is the case in which nickel sites does not deactivate by deposited carbon. For any reaction and in terms of activity, active metal should be straight forwardly approachable to the reactants. The active metal is carried on the top of the carbon filament and, as a consequence, the catalytic activity remains constant since the active metal is still accessible to the reactants. The stability was better with effect of MgO compare to ZrO 2 catalyst. Higher stability with MgO promoted catalyst was due to proper interaction among Ni and support, which results uniform dispersion of Ni particles, resistance to carbon deposition and sintering [22]. Bond between metal and support is strong, structure remains strong and if bond is not strong, structure remains weak, and then carbon formation via methane decomposition is more probable. Excellent stability of the catalyst can be ascribed to the uniform particle size distribution and to strong metal support interaction (SMSI) effect. 5. CONCLUSION The desirable catalyst with high specific surface area, uniform particle size distribution, high dispersion of active metal and strong metal surface interaction effect, is the most considerable efforts for DRM commercialization. Ni catalyst supported over alumina and different promoters like CeO 2, ZrO 2 and MgO were used for DRM. From our study, few conclusions can be drawn as below. According to results of characterization techniques and reactivity tests for promoted and un-promoted catalyst, prepared by co-precipitation method: 1. The optimum Ni (10%) loading gives higher conversion, it is due to small and well dispersed NiO crystals. The 10%Ni/5%ZrO 2 -Al 2 O 3 co-precipitated catalyst gives higher activity compare to other promoted and un-promoted catalysts prepared by same method. The 10%Ni/5%ZrO 2 -Al 2 O 3 catalyst displayed high catalytic performance for CO 2 /CH 4 reforming at 1073K because the small size of nickel particles maintained enough active sites on the surface of catalyst. 10%Ni/5%ZrO 2 - Al 2 O 3 catalyst gives higher H 2 /CO ratio compare to other two promoted catalyst and near to unity. 2. It has been observed that by increasing reaction temperature the percentage conversion of methane increase as DRM is endothermic. The present investigation 13 editor@iaeme.com

14 Sanjay P. Gandhi and Sanjay S. Patel confirms that at high GHSV the conversion of CH 4 and CO 2 in declined trend, as reactant does not have sufficient time to react over the surface of Ni. 3. In DRM reaction coke deposition over catalyst due to RWGS reaction and the dissociation of CH 4. Promoters (CeO 2, ZrO 2 and MgO) were used to avoid and control deactivation. The effect of CeO 2, ZrO 2 and MgO addition to Ni/Al 2 O 3 catalyst were studied to enhanced activity and stability of the prepared catalyst for dry reforming of methane. Deactivation was observed with all Ni catalyst supported on Al 2 O 3 and promoted CeO 2, ZrO 2 and MgO up to some extent. CeO 2 promoted catalyst exhibits comparatively constant recitation for 12 h on stream. 4. XRD measurement also indicates the introduction of CeO 2 enhances the dispersion of nickel particles and reducibility of Ni/Al 2 O 3 also increased and inhibited the formation of NiAl 2 O 4. Addition of CeO 2 in to 10%Ni/Al 2 O 3 system does not also suppressed the carbon deposition, because CeO 2 enhanced the Ni dispersion and reactivates of carbon deposition. REFERENCES [1] Nader Rahemi, M. Haghighi, A. A. Babaluo, M. F. Jafari, P. Estifaee, Synthesis and Physicochemical characterization of Ni/Al 2 O 3 -ZrO 2 nanocatalyst prepared via impregnation method and treated with non thermal plasma for CO 2, Journal of Industrial and Engineering Chemistry, 19 (2013) [2] Seyed Mehdi Sajjadi, M. Haghighi, Farhad Rahmani, Dry Reforming of greenhouse gases CH 4 /CO 2 over MgO-Promoted Ni-Co/Al 2 O 3 -ZrO 2 nanocatalyst: effect of MgO addition via sol-gel method on catalytic properties and hydrogen yield, Journal of Sol-Gel Science Technology (2014) 70: [3] Y. Vafaeian, M. Haghighi, S. Aghamohammadi, Ultrasound assisted dispersion of different amount of Ni over ZSM-5 used as nanostructure catalyst for hydrogen production via CO 2 reforming methane, Energy Conversion and management 76 (2013) [4] Nader Rahemi, M. Haghighi, A. A. Babaluo, M. F. Jafari, and Somaiyeh Allahyari, CO 2 reforming of methane over Ni-Cu/Al 2 O 3 -ZrO 2 nanocatalyst: The influence of plasma treatment and process conditions on catalyst properties and performance, Journal of Chemical engineering 31(9) (2014) [5] S. Therdhianwong, C. Siangchin, A. Therdthianwong, Improvement of coke resistance of Ni/Al 2 O 3 catalyst in CH 4 /CO 2 reforming by ZrO 2 addition. [6] Y. Vafaeian, M. Haghighi, S. Aghamohammadi, Ultrasound assisted dispersion of different amount of Ni over ZSM-5 used as nanostructure catalyst for hydrogen production via CO 2 reforming methane, Energy Conversion and management 76 (2013) [7] A. E. Castro Luna, M. E. Iriate, Carbon dioxide reforming of methane over a metal modified Ni-Al 2 O 3 catalysts, Applied Catalysis A: General 343 (2008) [8] Y. Vafaeian, M. Haghighi, S. Aghamohammadi, Ultrasound assisted dispersion of different amount of Ni over ZSM-5 used as nanostructure catalyst for hydrogen production via CO 2 reforming methane, Energy Conversion and management 76 (2013) [9] S. Aghamohammadi, M. Haghighi, S. Karimipour, A comparative synthesis and Physicochemical characterization of Ni/Al 2 O 3 -MgO Nanocatalyst via sequential impregnation and sol-gel methods used for CO 2 reforming of 14 editor@iaeme.com

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