Preparation of Ni-Zn-P Catalysts Supported on Polyurethane Foam by Electroless Deposition Method

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1 Paper Code: ms003 TIChE International Conference 2011 Preparation of Ni-Zn-P Catalysts Supported on Polyurethane Foam by Electroless Deposition Method Sara Ahmadi Pirshahid 1*,Yuttanant Boonyongmaneerat 2,Okorn Mekasuwandumrong 3, Joongjai Panpranot 1 1 Center of Excellence on Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, 10330, Thailand 2 Metallurgy and Materials Science Research Institute (MMRI), Chulalongkorn University, Bangkok, 10330, Thailand 3 Department of Chemical Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Nakorn Pathom, 73000, Thailand * lala_nano@hotmail.com Abstract The Ni-Zn-P catalysts supported by polyurethane foam were prepared by electroless deposition method with various zinc salt s contents in the deposition bath (6-24 g/l ZnSO 4.7H 2 O). The amounts of Ni and P in the bath were fixed at 42 g/l NiSO 4.6H 2 O and 24 g/l NaH 2 PO 2. The catalysts were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX) and X-ray photoelectron spectroscopy (XPS). Increasing amount of Zn in the bath resulted in lower rate of metal deposition; however, smaller nodular structure was obtained. The highest amount of Zn obtained in the final catalysts was 27.3 wt% with Ni and P 65.2 and 7.5 wt%, respectively. The catalytic properties of the Ni-Zn-P/PU foam were evaluated in the gas-phase hydrogenation of acetylene. Keyword: Ni-Zn catalyst, Electroless, Polyurethane, composites, Acetylene hydrogenation ms003 1

2 1.Introduction The commonly used methods for preparing supported metal catalysts include incipient wetness impregnation, precipitation, sol-gel, and vapor deposition. These methods, however, usually take long time for each step during preparation such as drying and calcination steps. Electroless plating is known to be one of the most frequently adopted methods to deposit metallic film on either conductive or nonconductive substrates because of its low cost, easy control, simplicity of processing, and applicability to complicated-shaped materials [1]. Recently, electroless deposition has been employed for preparation of supported metal catalysts such as Au- Pd/SiO 2 [2], Ag-Pd/SiO 2, Cu-Pd/SiO 2 [3], and Co-Ni-P [4], and studied in many catalytic reactions. In this study, Ni-Zn-P catalysts supported on polyurethane (PU) foams were prepared by electroless deposition method with different Ni/Zn ratios. The PU foams are porous materials with a special structure made of a skeleton of more or less regular open or closed cells. The unique properties of PU foams lie in their high surface area, lightness, and relatively low price. [1,5,6] The Ni-Zn bimetallic catalysts have been used in the steam reforming of methane, the production of synthesis gas and the selective hydrogenation [8]. Incorporation of Zn 2+ in the solid structure of Ni-Zn resulted in significant improvement in the catalytic properties in the selective hydrogenation of acetylene [7-8]. The catalysts were characterized by scanning electron microscopy and energy dispersive X-ray spectrometer (SEM-EDX), and X-ray photoelectron spectroscopy (XPS). 2. Experimental 2.1 Electrolyte preparation The Ni-Zn composites were prepared from the electroless bath of the following compositions: 42 g/l nickel sulfate (NiSO 4 6H 2 O), 102 g/l sodium citrate (C 6 H 8 O 7 Na 3 2H 2 O), 60g/l ammonium chloride (NH 4 Cl), 24 g/l sodium hypophosphite (NaH 2 PO 2 ), thiourea 0.01% with the amount of zinc sulfate (ZnSO 4 7H 2 O) was varied in bath then added into 250 ml distilled water. These experiments were performed at temperature of 85± 2 o C. The ph in bath was adjusted to 10 using sodium hydroxide (NaOH). The deposition conditions are summarized in Table 1. Table 1 Experimental conditions for electroless deposition Composition of electrolyte NiSO 4 6H 2 O (g/l) 42 ZnSO 4 7H 2 O (g/l) 6, 12, 18, 24 C 6 H 8 O 7 Na 3 2H 2 O (g/l) 102 NH 4 Cl (g/l) 60 NaH 2 PO 2 (g/l) 24 Thiourea 0.01% (ml/l) 4.8 Operating conditions ph 10 Tempreture ( o C) 85 Time (hr) Catalyst preparation The surface PU foam (0.06 g) was pretreated by dipping in 30% sodium hydroxide (NaOH) at 60 o C for 10 min. and washed with distilled water at room temperature. Then, it was dipped into 1g/l palladium chloride (PdCl 2 ), 50g/l stannous chloride (SnCl 2 ) and 1 mol/l hydrochloric acid solution at room temperature for 10 min. The PU foams were repeatedly washed with distilled water and dried with a blower. The electroless deposition was carried out in the electrolyte solution for 1 hr. 2.2 Deposition rate of Ni-Zn-P on PU foam The deposition rate of the alloys onto the PU foams was calculated by the following equation: v=(m 2 -m 1 )/(m 1 t) (1) where m 1 and m 2 are the masses of the PU foam before and after electroless plating procedure, respectively; t is the stabilizing time of electroless bath [9]. 2.3 Catalyst characterization The morphology and elemental composition of the samples were investigated by SEM and EDX using a JEOL JSM-35CF scanning electron microscope operated at 20 kv. Elemental composition on the catalyst surface was determined by XPS using an Amicus photoelectron spectrometer with Mg K α X-ray source. The binding energy was calibrated with the C 1s peak at ev. ms003 2

3 2.4 Reaction study The catalytic activity was evaluated in the gas-phase selective hydrogenation of acetylene in a 10 mm (id) pyrex reactor. The catalyst was reduced in situ in hydrogen flow by heating from room temperature to 90 o C with a heating rate of 10 o C/min. Then the reactor was purged with argon and cooled down to room temperature. The reaction was carried out using a feed composition of 1.5% C 2 H 2, 1.7% H 2, and balance with C 2 H 4. The reaction temperature was varied at 50, 60, 70, and 80 o C. The reactants and products were analyzed by two gas chromatographs equipped with FID detector (SHIMADZU FID GC 9A, cabosieve column S-2) and TCD detector (SHIMADZU TCD GC 8A, molecular sieve-5a) 3. Results and discussion 3.1 SEM and EDX analysis Surface morphologies of the PU foam supported Ni-Zn-P catalysts prepared by electroless deposition with various amounts of ZnSO 4 in the bath are shown Fig. 1. The three dimensional network of the PU foam microstructure was not much altered after electroless deposition of the metals. Some cracks were observed on all the PU foam samples due to the treatment with 30% NaOH. It is clearly seen that increasing the amount of ZnSO 4 concentration in the electroless bath decreased the amount of the metals deposited on the PU foams. However, smaller nodular structure appeared on the surface of the samples with higher amount of zinc. The EDX spectra of various Ni-Zn-P/PU catalysts are shown in Fig. 2. The contents of Ni, Zn, and P as a function of the amount of zinc in baht, as obtained from EDX measurements, are shown in Fig. 3. it was found that the content of ZnSO 4 in the Ni-Zn-P catalysts increased with increasing amount of ZnSO 4 in the bath from 6 g/l to 18 g/l with a maximum at 27 wt%. Further increase ZnSO 4 amount to 18 g/l and 24 g/l showed an opposite trend in which wt% of ZnSO 4 decreased to 22%. Fig. 1 SEM micrographs of Ni-Zn-P catalysts prepared by electroless deposition method with different amounts of ZnSO 4 in bath: (a) before supported (b) 6 g/l (c) 12 g/l (d) 18 g/l (e) 24 g/l ( 15 (left) and 400 (right)) ms003 3

4 Fig. 3 EDX results of PU foam after electroless deposition of the Ni- Zn-P sample with varied amount of ZnSO 4 in the bath. 3.2 Deposition rate of Ni-Zn-P on PU foam Fig. 2 EDX spectra of Ni-Zn-P catalysts prepared by electroless deposition method with various amounts of ZnSO 4 in bath (a) 6 g/l (b) 12 g/l (c) 18 g/l (d) 24 g/l Fig. 4a shows the deposition rate of Ni-Zn-P catalysts prepared with different amounts of ZnSO 4 as a function of deposition time. Much higher deposition rate was obtained when relatively low amounts of ZnSO 4 were employed. Fig.4 Deposition rate in electroless bath of Ni-Zn-P catalysts (a) Comparison of different amount of ZnSO 4 as a function of deposition time. (b) With various amount of ZnSO 4 in bath with deposition time 1 hr. In other words, the presence of zinc retarded the overall deposition rate of the metals during the electroless deposition of Ni-Zn-P alloys. ms003 4

5 Increasing the amount of ZnSO 4 from 6 to 12 g/l resulted in a sharp decrease of the deposition rate. Such effect became less pronounced at higher amounts of ZnSO 4 (Fig.4b). The optimum deposition time was determined to be 60 min. 3.3 XPS analysis XPS is a very useful tool to study the chemical states of the element on a solid surface [10]. The elemental scan of Ni 2p of the Ni-Zn-P catalysts prepared with the amount of ZnSO 4 18 g/l is shown in Fig. 5. The peak at binding energy ev was observed and was attributed to Ni 2+ ion [8]. Similar results were obtained for the other samples prepared with 6, 12, and 24 g/l ZnSO 4. It is thus suggested that nickel on the surface of Ni-Zn-P catalysts is present mostly in the form of nickel oxide. The XPS peaks corresponding to Zn 2p and P 2p were not detected in all the samples, despite the detection of elemental zinc and phosphorus from the EDX measurements. Fig. 6. Variation of acetylene conversion with the temperature of Ni- Zn-P catalysts with various amount of ZnSO 4 in bath may contribute to the improvement of the catalytic activity of the Ni-Zn-P alloys. 4. Conclusions The Ni Zn-P catalysts supported on PU foam were prepared by the electroless deposition method. The rate of deposition was decreased with increasing amount of Zn in the deposition bath. The maximum amount of Zn being able to deposit on the PU foam was 27.3 wt% using 18 g/l ZnSO 4. The highest catalytic activity in term of acetylene conversion was obtained on the samples with relatively high amount of zinc due probably to the formation of more refined surface morphology. References Fig.5. XPS spectrum of Ni 2p on the PU foam supported Ni-Zn-P catalyst prepared with the amount of ZnSO 4 in bath 24 g/l 3.4 Catalytic activity test The catalytic activity of the PU foam supported Ni-Zn-P catalysts was evaluated in the gas-phase hydrogenation of acetylene at the reaction temperature ranging from o C. The percentages of acetylene conversion from various catalysts are shown in Fig. 6. The acetylene conversion increased with increasing reaction temperature. The catalysts prepared with higher amount of ZnSO 4 in the baht (18 and 24 g/l) exhibited higher acetylene conversion than the ones prepared with lower amount of ZnSO 4.According to the SEM results, the use of higher amounts of ZnSO 4 resulted in a more characters [1] Tian Qing-hua, Guo Xue-yi, Xue Ping, Song Yu, Duan Lian, Materials Science Forum, 561/565(3) (2007) [2] Jayakiran Rebelli, Michael Detwiler, Shuguo Ma, Christopher T. Williams, John R. Monnier, Journal of Catalysis 270 (2010) [3] Melanie T. Schaal, Ashley Y. Metcalf, Joseph H. Montoya, J. Paul Wilkinson, Carol C. Stork, Christopher T. Williams, John R. Monnier, Catalysis Today 123 (2007) [4] T.S.N. Sankara Narayanan, S. Selvakumarb, A. Stephenb, Surface and Coatings Technology 172 (2003) [5] Kaplan, W. A. and Tabor, R. L., Cellular Polymers, 1993, 12, 102. [6] M. Thirumal, D. Khastgir, N.K. Singha, B.S. Manjunath, J. Appl. Polym. Sci. 108 (3) (2008) [7] Rives, V., Ulibarri, M.A., Montero, A., Appl. Clay Sci. 10, [8] J. C. Rodr ıguez, A. J. Marchi, A. Borgna and A. Monzón Santiago del Estero 2654, [9] TIAN Qing-hua, Guo Xue-yi, Electroless copper plating on microcellular polyurethane foam, Trans Nonferrous Met Soc China, 20, (2010), [10] Claude Guimona, et.al, Applied Catalysis A, 251 (2003) ms003 5