ROLE OF NANOPARTICLE SIZE ON PERFORMANCE OF PARTIAL OXIDATION OF BUTANE PROCESS TO SYNGAS

J. Chil. Chem. Soc., 62, Nº 3 (2017) ROLE OF NANOPARTICLE SIZE ON PERFORMANCE OF PARTIAL OXIDATION OF BUTANE PROCESS TO SYNGAS MAHDI.FAKOORI1*, BIZHAN.HONARVAR2 1 Department of Process, South Pars Gas Complex, Assalouyeh, Iran Department of Chemical Engineering, Marvdasht Branch, Islamic Azad University, Marvdasht, Iran 2 ABSTRACT In this study, performance of nano structure Co/γ-Al2O3 catalysts in partial oxidation of butane was investigated. The catalysts were produced through chemical reduction and incipient wetness impregnation methods. Prepared catalysts were characterized with X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM),N2 adsorption/desorption (BET), temperature programmed reduction (TPR) and thermal gravity analysis (TGA).The characterization results confirmed the uniform dispersion of Co nanoparticles over γ-Al2O3 by using chemical reduction. Butane conversion, H2 and CO selectivities increased by decreasing of Co particle size due to higher dispersion and reducibility. The optimum value of H2/CO ratio of 2 obtained from chemical reduction technique. The results showed that the stability of catalyst produced by chemical reduction method was higher than incipient wetness impregnation ones. Keywords: Partial oxidation, butane, Co/γ-Al2O3, particle size, selectivity. INTRODUCTION In recent years, a catalytic partial oxidation of butane has attracted much attention because the reaction can produce H2/CO ratio of 2 which is suitable for feed of Fischer–Tropsch reaction [1]. It is well known that high butane conversion, H2 and CO selectivities can be obtained over catalysts containing transition metals (Ni, Co, Cu and Fe), noble metals (Pt, Pd, Rh, Ru and Ir) and metal oxides [2].Among those, the catalysts based on noble metals are more active than Co-based catalysts. However, because of the very high cost of noble metals, Co-based catalysts are usually used for butane reforming reactions especially due to their low cost [2]. One of the important parameters in catalytic reactions is particle size of active species. Iglesia [3] reported a significant increase in the activity of Fischer-Tropsch synthesis reaction when the cobalt particle size was decreased from 50 to 9 nm. The particle size has a important role on the interaction between cobalt species and support, Therefore it can influences on the reducibility of cobalt species [4]. Hence the methods of catalyst synthesis result in the uniform size, homogeneous distribution and higher reducibility of metal species are important factors for the higher activity in partial oxidation of butane [4]. Sun et al. [5] reported the preparation of Co/SiO2 catalyst with high cobalt dispersion through the mixture cobalt acetate and cobalt nitrate precursors and reached to higher number of active sites. Bezemer et al. [6] investigated the effect of particles size of Co/CNT catalyst on the performance of FTS reaction and founded that optimum conditions obtained by particles larger than 5-6 nm. Mosayebi and abedini. [1] reportd the synthesize of Ni/Zeolite catalyst with size-controlled Ni nanoparticles by using microemulsion method and reached to high degree of reducibility. In recent years, the chemical reduction method for catalyst synthesis used in different catalytic process by scholar [7]. This technique led to uniform distribution and higher dispersion (smaller particle size) of metal species and finally increase in reactants conversion and selectivity of desired products. In this study, the Co/γ-Al2O3 catalysts prepared by using chemical reduction method and its structural properties, performance in partial oxidation of butane was compared with catalyst produced through incipient wetness impregnation technique, which was no reported in the literature since now. EXPERIMENTAL Catalyst preparation In first method, the Co/γ-Al2O3nano-structure catalysts were synthesized using a chemical reduction. In detail, 0.5 g of γ-Al2O3 (Merck) was dispersed in 60 ml ethanol–water (Volume ratio = 1:1) solution by ultrasonic at 323 K for 30 min. Then, 0.025 g of CoCl2.6H2O (Sigma Aldrich) aqueous solution was added into the suspension, stirred and purged by N2 for 90 min. Suspension was saturated of N2, NaBH4 prepared solution as reducing, is added dropwise into the solution under stirring at room temperature. After the suspension stirred for 12 h. The solid sample is filtrated using circle filtration paper and washes several times with ethanol and deionized water. The catalysts are dried in vacuum condition at 373 k for 12 h. In order to remove impurities and residuals, the catalysts are calcined at 773 k for 6 h. e-mail: In second method, Nano-structure Co/γ-Al2O3 catalyst were synthesized using an incipient wetness impregnation.Co(NO3)2.6H2O. At first, Co/γ-Al2O3 was prepare using the dispersion of γ-Al2O3 powder (Merck) in an aqueous solution (30 mL) of Co(NO3)2.6H2O (Merck) as a Co precursor. Then, solution stirred for 2 h followed by drying at 100 °C in vacuum condition for 12 h.In order to remove the impurities, the catalysts were calcined at 500 °C for 4 h. In each two synthesize technique, Co loading was 20 wt.%, which verified by an Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) system.The Co/γ-Al2O3 catalysts prepared through chemical reduction and incipient wetness impregnation were noted as CR and IW, respectively. Characterization of the catalysts The surface area and pore volume of the catalysts were measured by an ASAP-2000 system from Micromeritics. The samples were degassed at 250 °C for 3 h under 70 mTorr vacuum and their BET area and pore volume were determined. For Ni/ZSM5, Ni/Y and Ni/Mordenit, X-ray diffraction patterns were obtained with an X-ray diffractometer (D/max-rB 12 kW Rigaku, Japan; 45 kV, 40 mA) operated at 50 mA and 50 kV from 108 to 808.The TPR experiment is carried out using Quantachrome chemBET-3000 so that the 0.05 g of catalyst is placed in a quartz tubular reactor. Prior to the temperatureprogrammed reduction measurement, the calcined catalysts are heated to 150 °C in a pure N2 steam and held at this temperature for 30 min in order to remove water or impurities. The sample is then cooled down to the room temperature in N2 and the gas is switched to 5% H2/Ar, then catalyst temperature increases to 1073 k at 10 k. min-1. The morphology of catalyst is specified using Philips CM30 high resolution transmission electron microscopy (HRTEM).Thermo gravimetric analyses (TGA) of prepared catalysts after FTS reaction were conducted by using TGA/SDTA851e apparatus to investigate the carbon deposition on the catalysts. The test was carried out in an air flow of 50 ml/min in the range of 300 K to 1000 K at a rate of 30 K/min. reactions testing The partial oxidation of n-C4H10 was performed in a fixed-bed reactor. The schematic representation of the set up used is shown in Fig. 1. The reactor (ID = 30 mm, OD = 35 mm and L= 70 cm) was made of 316 stain (...truncated)