Environment, National University of Malaysia, Bangi, Selangor, Malaysia * Corresponding Author

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1 AMERICAN JOURNAL OF SCIENTIFIC AND INDUSTRIAL RESEARCH 2010, Science Huβ, ISSN: X doi: /ajsir Short communication Hydroxyapatite supported Nickel catalyst for hydrogen production Zahira Yaakob* 1,2, Lukman Hakim 1, M.N. Satheesh Kumar 2, Manal Ismail 1, 2 and Wan Ramli Wan Daud 1,2 1 Fuel Cell Institute, National University of Malaysia, Bangi, Selangor, Malaysia 2 Department of Chemical & Process Engineering, Faculty of Engineering & Built Environment, National University of Malaysia, Bangi, Selangor, Malaysia * Corresponding Author zahirayaakob@gmail.com ABSTRACT Hydroxyapatite (HAp) supported Nickel (Ni) catalyst was prepared using wet impregnation method. A series of Ni/HAp catalysts have been prepared by varying the amount of nickel viz., 3, 6 and 12 %. The highest Brunauer-Emmett-Teller (BET) surface area of m 2 /g was noticed for a catalyst composition containing 3% nickel loading. The scanning electron microscopy (SEM) studies revealed a smooth and compact morphology with increasing the nickel loading in the catalyst composition. The performance of the prepared catalysts have been evaluated in steam reforming glycerol process. The percentage hydrogen yield found to depend on water to glycerol ratio employed in the steam reforming process. The catalyst containing 3% nickel content and a water to glycerol ratio of 8:1 has showed a maximum hydrogen yield of 82.2%. Keywords: Glycerol, Steam reforming, Ni-hydroxyapatite catalyst, impregnation, hydrogen production. INTRODUCTION Fossil fuel, a major energy source is contributing to meet the day to day energy requirements. The diminution of fossil fuel reserves and increased green house gas emissions have directed the global research to capture the potential benefits of hydrogen economy from renewable resources [1-3]. Hydrogen is considered nowadays as an alternative fuel and its use is gaining more and more acceptance as the negative impact of petroleum fuels on the environment becomes more evident. The production of hydrogen is a subject of current interest for fuel cell or electricity production applications. Hydrogen based fuel cells are an alternative to internal combustion engines which run on petroleum based hydrocarbon fuels. As the hydrogen fuel cells are energy efficient and produce only water and heat, it can minimize the global energy and environmental problems [4]. Hydrogen is also an important material in chemical synthesis and refinery for clean fuel production. Glycerol is a by-product obtained during the production of biodiesel. The transesterification of vegetable oils or fats in presence of catalyst produces biodiesel along with glycerol as a byproduct [5]. The process of converting the vegetable oil into biodiesel results in more than 10% glycerol as a by-product. Glycerol appears to be a more promising source to produce hydrogen due to the fact that one mole of glycerol can produce up to 4 moles of hydrogen [6]. The steam reforming process is the efficient method to convert glycerol into hydrogen in presence of catalyst. In the steam reforming of glycerol, synthesis gas (syngas) containing carbon monoxide (CO) and hydrogen is produced. The steam reforming process of glycerol involves a complex reaction and as a result of that several intermediate products are formed. The overall reaction of steam reforming of glycerol is [7, 8]; C 3 H 8 O 3 3 CO + 4H 2 (1) CO + H 2 O CO 2 + H 2 (2) C 3 H 8 O 3 + H 2 O 3 CO H (3) 2 The steam reforming process of glycerol produces H 2, CH 4, CO, CO 2 and C together with the unreacted water and glycerol. CH 4 is expected to compete with H 2 and obviously it is not a desirable product. Since the decomposition of glycerol to CH 4 is highly favourable during the reforming process, the catalyst must have sufficient capacity for reforming the produced CH 4 into H 2 and CO [9]. The investigations related to the use of noble metal catalyst supported on Al 2 O 3, CeO 2 and La 1 x Ce x NiO 3 in the steam reforming of glycerol have been reported in the literature [10]. Nickel, a known transition metal was

2 employed in the catalytic processes such as decomposition, steam reforming and or partial oxidation of methane [11-14]. Hydroxyapatite [(Ca 5 (PO 4 ) 3 (OH)] has received considerable attention due to its ion-exchange ability, adsorption capacity, macroligand behaviour and acid-base properties [15]. Hydroxyapatite (HAp) is widely used as an implant materials in clinical applications owing to its biocompatibility. Apart from the clinical applications, HAp has also been used as a novel support for gold ruthenium catalysts employed in water gas shift reactions [16], as catalyst for dehydrogenation and dehydration of alcohols and also in photocatalytic applications [17]. Though Ni/HAp catalysts have been employed in catalytic decomposition of methane (CDM) to obtain pure hydrogen [18], the literature lacks the information related to the use of Ni supported HAp catalyst to obtain hydrogen via steam reforming of glycerol. The present research investigation concentrated to study the effect of different amounts of Ni loading in Ni/HAp on the BET surface area and morphology. The performance of the catalysts have been evaluated by subjecting into steam reforming process of glycerol. The performance of the catalysts have been evaluated by determining the total conversion of glycerol to hydrogen in the steam reforming process. EXPERIMENTAL Preparation of the catalysts: Nickel nitrate hexa hydrate [Ni (NO 3 ) 2. 6H 2 O] and hydroxyapatite (HAp) were obtained from Sigma-Aldrich. The Ni catalyst supported on HAp were prepared by wet impregnation method as described elsehwere [19]. A sereies of catalysts having differfent amount of Ni loadings viz., 3, 6 and 12 % by weight over HAp were prepared. The solutions were dried with constant stirring at C unitll the sample gets dried. The dried samples were kept in an oven maintained at C for a duration of 12 h. Finally, the dried catalyst were calcinined in static air at C. Catalyst characterization: The surface area of the prepared catalysts were characterized using BET measurements. The samples were treated at 120 ºC for 30 min to ensure a clean surface prior to the adsorption isotherm test. The specific surface area of the calcined catalyst samples were calculated from the acquired nitrogen (N 2 ) adsorption-desorption data. The scanning electron microscopy (SEM) combined with energy dispersive X-ray micro analysis (EDX) was performed using FESEM SUPRA 55VP. This technique can give the information about the morphology and the composition of the catalyst. Catalyst performance test: The ability of HAp supported Ni catalysts to convert glycerol into hydrogen in steam reforming process has been investigated. All experiments were performed in a tubular reactor which could reach temperatures up to C. Water at a flow rate of 0.04 ml/min and glycerol at a flow rate of ml/min was introduced into the fixed bed micro reactor using PHD 440 syringe pump. The tubular reactor made of stainless steel having 39 mm length, 6.35 mm diameter and 0.9 mm wall thickness was used. 0.5 g of the catalyst powder was placed in the middle of the reactor tube supported by quartz wool. Before activation, each catalyst was heated for 30 min at C. The catalysts were activated in situ by reducing in a N 2 flow of 35 ml/min with 10% H 2 for 1 h. Steam reforming experiments were performed at C under atmospheric pressure for 3 h. RESULTS AND DISCUSSION The effect of various amounts of nickel loading over HAp on the BET surface area of the catalysts are given in Table 1. The result of surface area is one of the major contributive factor governing the catalyst activity [20]. The catalyst containing 3% Ni over HAp exhibited higher surface area (92 m 2 /g) as compared to 6 and 12% Ni containing catalyst samples. The catalyst with high surface area is expected to accelerate the steam reforming reaction and as a result of this, a maximum conversion of glycerol into hydrogen can be expected. Table 1. The surface area of Ni/Hap catalyst Catalyst 3% Ni/HAP % Ni/HAP % Ni/HAP Surface area (m2/g) SEM-EDX investigation was employed to investigate the dispersion of Ni on HAp support. In general, a homogeneous dispersion of the catalysts can be observed from the SEM images [Figure 1(a) - (c)]. This can be attributed to the good impregnation of Ni over HAp. A smooth and compact surface morphology can be observed with increasing the Ni content in the catalyst composition. This may be due to different sintering behaviour with increasing the Ni content in the catalysts. It appears that, relatively, 3% Ni supported HAp catalyst [Figure 1 (a)] found to have more surface area than other catalysts. SEM microphotograph with micro analysis data clearly 123

3 exhibited the Ni and Ca peaks. The amount of Ni content present in the catalyst can be confirmed from the EDX data. Fig 1. SEM and EDX analysis of catalysts having different amount of Ni content viz., (a) 3, (b) 6 and (c) 12%. Catalytic conversion of glycerol to hydrogen involves the preferential cleavage of C-C bonds as opposed to C-O bonds [21]. It is generally accepted that nickel promotes C-C rupture [22]. Since steam reforming of glycerol is a highly endothermic reaction, high temperature favours glycerine conversion. The performance of the catalyst in steam reforming reaction at C and atmospheric pressure as a function of Ni content (3, 6 and 12% on HAp support), reaction time and water to glycerol ratio (4:1 and 8:1) on the hydrogen yield is given in Figure 2 (a) and (b). The hydrogen yield was calculated using the equation; 124

4 H 2 Yield = Hydrogen yield (mol %) Hydrogen Yield (mol%) H 2 moles produced Maximum moles of H 2 (=7) x 100 (4) 3% 6% 12% (a) Time (min) Time (min) 3% 6% 12% Fig 2. Percentage hydrogen yield of Ni/HAp catalysts having 3, 6 and 12% Ni content as a function of reaction time and water to glycerol ratio of (a) 4:1 and (b) 8:1 The H 2 yield found to increase with increase in the steam reforming reaction time ( min) irrespective of different water to glycerol ratio (4:1 and 8:1) for all the catalyst samples. Compared to 6 and 12% Ni loaded HAp catalysts, 3% one showed highest H 2 yield of and 82.19% for a water to (b) glycerol ratio of 4:1 and 8:1 respectively. It is expected that with increasing the water to glycerol feed ratio, an increase in the number of moles of hydrogen due to the presence of large amount of water. The observed maximum H 2 yield with 3% Ni loaded HAp catalyst was % (8:1 water to glycerol ratio). This may be due to the highest BET surface area (Table 1) which is responsible for increased catalytic activity. The investigation of Adhikari et al [20] on steam reforming of glycerol revealed a H 2 yield of 44-56%, 31-33% and 31-47% at 550, 600 and C using Ni/MgO, Ni/CeO 2 and Ni/TiO 2 catalyst systems respectively [19]. In an work on steam reforming of glycerol using Ni/Al 2 O 3 exhibited a glycerol conversion of 82% at C [23]. Conclusions: The effect of various amounts of Ni in Ni/HAp catalyst system on the surface area, morphology and its performance in steam reforming of glycerol have been investigated. Highest surface are of m 2 /g was noticed with Ni/HAp catalyst containing 3% Ni content. A smooth and compact morphology can be observed with increasing the Ni content in the catalyst. The EDX data confirmed the amount of Ni present in the catalyst composition. The obtained maximum H 2 yield was 82.19% with the Ni/HAp catalyst containing 3% Ni and 8:1 water to glycerol feed ratio. ACKNOWLEDGEMENTS: The authors gratefully acknowledge the financial support from National University of Malaysia under grant UKM-OUP-TK-16-72/2009 REFERENCES Adhikari S, Fernando SD, Haryanto A. Hydrogen producito from glycerin bys steam reforming over nickle catalysts. Renewable energy 2008; 33: Adhikari S, Fernando SD, Haryanto A. Production of hydrogen by steam reforming of glycerine over aluminasupported metal catalysts. Catalysis Today 2007; 129: Ashok J, Naveen Kumar S, Subrahmanyam M, Venugopal A. Pure H 2 Production by decomposition of methane over Ni supported on hydroxyapatite catalysts. Cata Lett 2008; 121: Conte M, Iacobazzi A, Ronchetti M, Vellone R. Hydrogen economy for a sustainable development: state-of-the-art and technological perspectives. J Power Sources 2001; 100: Cortright RD, Davda RR, Dumesic JA. Hydrogen from catalytic reforming of biomass-derived hydrocarbons in liquid water. Nature 2002; 418:

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