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

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International Journal of Advanced Research in Engineering and Technology

(IJARET) Volume 6, Issue 11, Nov 2015, pp. 01-17, Article ID: IJARET_06_11_001 Available online at http://www.iaeme.com/IJARET/issues.asp?JType=IJARET&VType=6&IType=11 ISSN Print: 0976-6480 and ISSN Online: 0976-6499 © IAEME Publication

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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 H2 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 H2 to CO ratio is

required and important, as it is a most likely feedstock. In recent decades, CO2 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 CH4 and CO2 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 ZrO2, CeO2 and MgO, in the

performance of Ni-Al2O3 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: CH4/CO2 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



Journal of Advanced Research in Engineering and Technology, 6(11), 2015, pp. 01-17.

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1. INTRODUCTION

Utilization of CO2, via a reaction with CH4 to produce a mixture of CO and H2 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 H2/CO ratio, is suitable for use in forming higher levels alcohols. Typical application is production of methanol and fischer-tropsch synthesis H2/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 CO2 and CH4 and are good candidates for dry reforming of methane. CO2 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 CO2 and H2. Because of RWGS reaction the overall CO2 conversion greater than CH4. Carbon deposition via boudouard reaction (3) and methane decomposition (4) can deactivate the catalyst are major problems in catalytic CO2

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

Syngas Production by Dry Reforming of Methane over Co-Precipitated Catalysts


based catalyst are first in choice for the CO2 reforming due to its activity and reasonable price [4, 5]. Basically, support selection is important, as control of the Ni-

support interactions can improve Ni-catalyst activities in CO2 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 La2O3, MgO, CaO, SiO2 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 co-precipitation 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 Na2CO3 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.

2.2. Catalyst activity

The CO2 reforming of methane was carried out at 923-1073 K and atmospheric pressure, using 1 gm catalyst in a stainless steel tubular fixed-bed reactor. Fixed bed reactor having tube of 18.05 mm inner, 19.05 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 CH4 :CO2:N2 – 1:1:1 with total flow rate of 500 ml/min having GHSV of 30000 cm3 /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.

XCH4% = [CCH4in-CCH4out]/ CCH4in * 100

XCO2% = [CCO2in-CCO2out]/ CCO2in * 100

YH2% = CH2out/2CCH4in*100

YCO% = CCOout/[CCH4in+CCO2in] * 100



Where Xi and Yi are the conversion of reactants and yields of products, respectively Ciin is the initial molar fraction of component i in the feed, and Ciout 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, Ho lland 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].

3.2. 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 po,

The amount of gas adsorbed at the relative pressure p/po, : na

The monolayer capacity, and C is the so-called BET constant: nam

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.

3.3. 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

http://en.wikipedia.org/wiki/Infrared

http://en.wikipedia.org/wiki/Electromagnetic_spectrum

http://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)

http://en.wikipedia.org/wiki/Emission_(electromagnetic_radiation)

http://en.wikipedia.org/wiki/Photoconductivity

http://en.wikipedia.org/wiki/Raman_scattering



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%CeO2-Al2O3 and 10%Ni/5%MgO-

Al2O3

The XRD patterns for Al2O3 supported, prepared by co-precipitation, 5%Ni, and with different promoters (CeO2 and MgO) are shown in Fig. 1 and 2. The Al2O3, Ni, NiO,

CeO2, MgO, NiAl2O4 and MgAl2O4 phases were detected in the XRD patterns. By increase of nickel loading the ratio of NiO intensity to Al2O3 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 NiAl2O4 phase [9].

According to the JCPDS files, the Al2O3, Ni, NiO, CeO2, MgO, NiAl2O4 and MgAl2O4 phases can be detected in the XRD patterns [15]. NiO diffraction peaks

observed at 2 37.3, 43.4, 44.5, 62.9, 63.0, 75.6 and 79.6. 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 MgAl2O4 and NiAl2O4 respectively [7-9]. The smaller amount of Ni interact with alumina and form nickel aluminate (NiAl2O4)

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 NiAl2O4

is smaller than the recognition limit of XRD.

Figure 1 X-Ray diffraction pattern of the catalyst 10%Ni/5%CeO2-Al2O3

In Fig. 1, the XRD patterns of 10Ni/5%CeO2-Al2O3 shows intense diffraction

lines of NiO (2θ= 43.2°), Al2O3 (2θ = 66.3°) and CeO2 (2θ = 29°, 57°). In this catalyst single major phases of alumina and crystalline phase of nickel and two of phases of CeO2 were detected. The amount of CeO2 addition influenced the intensities of

http://en.wikipedia.org/wiki/Dispersion_(optics)



Nickel peaks. The weaker and broader the Ni Peak due to the more CeO2 loading on catalyst. It indicates that addition of CeO2 effects the nickel dispersion on catalyst.

Figure 2 X-Ray diffraction pattern of the catalyst 10%Ni/5%MgO-Al2O3

The overlap of alumina and nickel oxide form composite layer of NiO-Al2O3 which is an amorphous phase. The smaller amount of Ni particle interacts with alumina and form nickel aluminate (NiAl2O4). It is clear that strong interaction of

nickel metal and alumina lattice to make spinel type solid solution of NiAl2O4. There is NiAl2O4; 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 CeO2 and in

contrary, alumina peaks lost their intensity after introduction of CeO2. According to XRD patterns, big crystal of CeO2 was observed.

In Fig. 2, the XRD patterns of 10%Ni/5%MgO-Al2O3 shows intense diffraction lines of NiO (2θ= 62.7°), Al2O3 (2θ = 42.8°) and MgO (2θ = 74.8°, 78.7°). As Ni2+, Mg2+, Al3+, fall in to the same lattice, the formation of solid solution of spinel type of

MgAl2O4 and NiAl2O4 is favored under high temperature calcination. As Ni2+, Mg2+, Al3+, fall in to the same lattice, the formation of solid solution of spinel type of

MgAl2O4 and NiAl2O4 is favored under high temperature calcination.

4.2. BET Surface Area

The surface area, pore size and pore volume of the catalysts containing 5%, 10% Ni by weight and promoted with CeO2 are presented in table 1.

Table 1 Physical properties of catalysts.

Catalyst BET Surface Area

(m2/g)

Pore Volume

(cm3/g)

Pore Diameter

(nm)

5%Ni/Al2O3 142.56 0.24 5.31

10%Ni/Al2O3 130.19 0.20 5.65

10%Ni/5%CeO2-Al2O3 105.21 0.18 6.10



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.

4.3. 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 400-4000 cm-1.

Figure 3 FTIR Spectra of 10%Ni/CeO2-Al2O3.

Figure 4 FTIR Spectra of 10%Ni/ZrO2-Al2O3.

The IR spectra in all cases, exhibit metal-oxygen stretching frequencies in the range 470-900 cm-1 associated with the vibration of M-O, Al-O and M-O-Al bonds (M=Ni, CeO2, and ZrO2). 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.



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, ZrO2, and CeO2) 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/Al2O3 catalyst

presented in terms of feed conversion and product yields in Fig. 05, 06 and 07.

Figure 5 CH4 conversion (%) over different temperature (K) in Dry Reforming of methane.

As Ni loading increased up to 10% conversion of both CH4 and CO2 were considerably increased. At low Ni- loading conversion of CH4 and CO2 were

observed low, due to the small active nickel metal and the formation of NiAl2O4 even though their surface area is relatively high compared to 10%Ni loading.

When Zirconia added, both CH4 and CO2 conversions were strongly increased. It

is proposed that the presence of ZrO2 inhibits the NiAl2O4 formation. Further the Al2O3 surface is changed due to ZrO2 and Ni is not placed straight onto the Al2O3 but

near to ZrO2, as a result CO2 dissociation increase. Similar results and explanations were also found by Seo et al. [42], explaining that ZrO2 inhibits the inclusion of nickel species into the lattice of Al2O3, preventing the growth of metallic nickel

particles during the reaction step.



Figure 6 CO2 conversion (%) over different temperature (K) in Dry Reforming of methane.

Figure 7 H2/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%ZrO2-Al2O3 was high. Pompeo et al. also [11] explained the coke reduction capability of ZrO2 similar to our results.

It is also noticeable that CeO2 promoted catalyst has superior CH4 conversion then unsupported at all temperature. There are two main causes for same (1) CeO2 has higher

surface basicity compare to alumina and the formation of different types of carbonate like species due to interaction of CeO2 with CO2. [18] (2) CeO2 has oxidative properties and a good capacity for oxygen storage reaction [12]. With effect of CeO2; carbon

generated from CH4 dissociation and on catalyst; carbon atom reacted with oxygen-containing species from the dissociation. Due to the faster reaction rate of carbon



species formed on Ni/CeO2-Al2O3 catalyst, these system exhibits higher activity than Ni/Al2O3 catalyst. The converge of Ni metal by CeOx species induced by strong metal

surface interaction and the dispersive ability of CeO2 preventing the formation of large metal ensembles reduced the carbon deposition on Ni/ CeO2-Al2O3.

It is worth noting that, excellent performance of MgO in raising of basic sites concentrations and consequently, promoting the adsorption rate of acidic CO2 [13]. In presence of MgO, there is formation of MgAl2O4 phase and surface rearrangement

lead to improvement in catalytic activity [14].

Xu et al [43]. reported that NiO-MgO-Al2O3 catalyst was displaying high catalytic

activity and long catalytic stability. Monica Garcia-Dieguze et al [44]. expressed that the Mg incorporation to Ni/Al2O3 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 Ni-containing MgAl2O4 and NiAl2O4 phase due to the increased resistance against

physical degradation, but coking was found to decrease activity.

4.5. Effect of temperature

For all co-precipitated catalyst the consequence of temperature on the conversion of

reactant and product gas (H2 and CO) yields are given in Fig. 05 to 07. DRM is highly endothermic reaction as temperature increased conversion of CH4 and CO2 is increased and also the yields of H2 and CO [21].

Over all the catalyst and all examined temperatures, the conversions of CO2 were higher than those of CH4 which can be due to the existence of RWGS (reaction 2) reaction. Highest 76.55% and 80.13% conversion of CH4 and CO2 achieved at 1073 K

respectively with 10%Ni loading with effect of ZrO2. The RWGS is also contributed to higher CO2 conversion then CH4 conversion at low temperature, as reported [17].

CH4 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 CH4 dissociation is a strongly favoured reaction. The increase of CH4

dissociation is demonstrated not only in terms of feed conversion but also the coke yield. This suggests that the CH4 decomposition dominates the CO2

disproportionation for the coke formation at high temperatures, as was thermodynamically calculated by S. Therdhianwong et al [18]. Increase in H2/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 CO2 at higher temperature.

4.6. Effect of GHSV

Results in Fig. 8 & 9 show the influence of space velocity on catalytic activity for the reaction conversion and H2/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 CH4 and CO2 reforming reaction were conducted at constant

temperature of 1073 K. By increasing GHSV form 30000 to 48000 cm3/g*h both CH4 and CO2 conversion decrease. As the space velocity increase, yields of H2 and CO decrease.



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 CH4 and CO2 conversion, similar to observation of Mark and Maier [20]. According

to our results, an increase in GHSV has converse outcome for CH4 and CO2 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 H2 and CO yields decreases as GHSV increases for all catalyst.

Figure 8 CH4 (%) and CO2 (%) conversion over different GHSV (cm3/g*h).

Figure 9 H2/CO ratio over different GHSV cm3/g*h



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 co-

precipitated 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

CH4 and CO2 conversion after 12 h (720 min) of time on stream (C12=C1) ratios were 0.78, 0.73, 0.74 for 10Ni%/5%CeO2-Al2O3, 10Ni%/5%ZrO2-Al2O3 and

10Ni%/5%MgO-Al2O3 respectively.

Figure 10 Comparison of stability test of different catalyst over time (h) in terms of CH4 conversion (%)

Figure 11 Comparison of stability test of different catalyst over time (h) in terms of CO2 conversion (%)



The stability was better over the CeO2 promoted catalyst compared to other promoted catalysts. It was clear from results that good stability of the 10%Ni/CeO2-

Al2O3 catalyst compared to ZrO2 and MgO promoted catalyst. ZrO2 and MgO promoted catalysts indicate reducing trend in conversion of reactant and product

yield. The rate of the atomic carbon gasification by CO2 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 ind icated that the CH4 decomposition occurs on the surface of the active metals while CO2 adsorption take

place on the support. Adsorbed CO2 reacts with carbon species derived from dissociative adsorption of CH4. 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 ZrO2 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 CeO2, ZrO2 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%ZrO2-Al2O3 co-precipitated catalyst gives higher activity compare to other promoted and un-promoted catalysts prepared by same method. The 10%Ni/5%ZrO2-Al2O3 catalyst displayed high catalytic performance for CO2/CH4 reforming at 1073K because the small size of nickel particles maintained enough active sites on the surface of catalyst. 10%Ni/5%ZrO2-Al2O3 catalyst gives higher H2/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



confirms that at high GHSV the conversion of CH4 and CO2 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 CH4. Promoters (CeO2, ZrO2 and MgO) were used to avoid and control deactivation. The effect of CeO2, ZrO2 and MgO addition to Ni/Al2O3 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 Al2O3 and promoted CeO2, ZrO2 and MgO up to some extent. CeO2 promoted catalyst exhibits comparatively constant recitation for 12 h on stream.

4. XRD measurement also indicates the introduction of CeO2 enhances the dispersion of nickel particles and reducibility of Ni/Al2O3 also increased and inhibited the formation of NiAl2O4. Addition of CeO2 in to 10%Ni/Al2O3 system does not also suppressed the carbon deposition, because CeO2 enhanced the Ni dispersion and reactivates of carbon deposition.

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