Uniform Ni particles on amino-functionalized SBA-16 with excellent activity and stability for syngas methanation

https://doi.org/10.1016/j.molcata.2016.03.028Get rights and content

Highlights

  • Amino-functionalized mesoporous material SBA-16 was prepared by silylation.

  • Uniform size of nickel particles were observed on the modified material.

  • Better thermalstability and long-term stability were achieved for Ni/SBA-16-NH2 catalyst.

Abstract

Via modification of mesoporous material SBA-16 with silane coupling agent, a new functionalized SBA-16 catalyst immobilized Ni has been prepared. The performance of the catalyst for CO methanation then were systemically investigated in a continuous flow fixed-bed reactor. The as-synthesized catalyst was characterized with N2 absorption-desorption, X-ray diffraction, Transmission electron microscopy (TEM), FT-IR spectrum, 29Si-nuclear magnetic resonance (NMR), H2—Temperature Programmed Reduction (TPR) and H2 pulse chemisorption. After modification by aminopropyl-trimethoxysilane (APTMS), the internal surface silanol group of support SBA-16 was replaced by amino-groups. The replacement of hydroxyl groups by amino groups could prevent the agglomeration of metal ion in the solution. Also uniform nickel particle size was observed because the replaced organic groups on SBA-16 could form homogeneous interaction towards the metal. Comparing with the catalyst without functionalized, the catalyst Ni/SBA-16-NH2 exhibited higher activity, excellent heat-resistant performance and better stability in CO methanation. The CO conversion and CH4 selectivity could be 100% and 99.9% at the optimal temperature. Meanwhile, the catalyst showed no decrease of activity in the 100 h life test.

Introduction

Natural gas, a clean and efficient energy, has received more attention due to its high caloric value and environmental friendlessness [1]. In recent years, due to the rise of natural gas price, the wish for less dependency on natural gas import, and replacement of oil products, synthetic or substitute natural gas (SNG) production from renewable or syngas from coal is attracting attention in some developing countries. Among different fossil fuels, natural gas that consists primarily of methane is ideal, owing to its ready availability, high energy density and conversion efficiency. Meanwhile, natural gas can be transported efficiently at low cost using existing natural pipelines. Therefore, coal to natural gas(SNG) has been investigated deeply because of the " rich in coal, poor in oil and natural gas” energy landscape in China [2]. And recently severe environmental problems occurred in China due to the combusting of coal. In this situation, coal to synthetic natural gas (SNG) has attracted more and more attention. CO methanation reaction is one of the key reactions in the coal-to-SNG process and the catalyst design is the hard core of the reaction. Therefore, it would be worthwhile to develop an efficient catalyst for the methanation reaction. For the production of SNG, the CO methanation (CO + 3H2 = CH4 + H2O) is a key reaction which is highly exothermic and thermodynamically feasible [3]. Due to the property of the reaction, catalysts with high activity and stability in high temperature is of vital importance.

Generally, nickel-based catalyst has been widely employed in CO methanation because of its low price and relatively high activity. However, poor stability caused by carbon deposition and aggregation of active nickel in high temperature limited the industrial application [4], [5]. Therefore, development of catalyst with high activity and excellent stability is the purpose of the research. In previous work, it is found that SBA-16 was a good support to impregnation metal species because it has large surface area, tunable cage size (4–10 nm) and interconnected nanocage [6]. However, the catalyst prepared by SBA-16 revealed poor stability at high temperature. In order to solve the problem, one solution is to select a promoter metal such as Mo, Ce, Mg and Pt to produce a synergistic effect with Ni, which was investigated deeply in recent research [3], [7], [8], [9], [10].However, the introduction of the noble metal may cause an environmental problem, which was difficult for recycle. Another popular method to improve the stability of catalyst is the modification of the support [11], [12], [13]. Recently, induction of organo-functional groups to ordered mesoporous silica by silylation have achieved more attention in many fields, such as catalysis, separation and absorption [14], [15], [16], [17]. After silylation by organosilanes such as aminopropyl-trimethoxysilane (APTMS), the hydrophobic and hydrophilic nature of mesoporous silica surface was drastically changed, because the hydrophilic silanol group was replaced by hydrophobic chloroalkyl chains through silylation. Jianwen Wei et al. found that amino-functionalized SBA-16 showed high hydrothermal stability and thermal stability comparing with SBA-16 [18]. Via modification of mesoporous material SBA-16 followed by absorption of Pd(OAC)2, the catalysts exhibited excellent activity and recyclability for the aerobic oxidation of alcohols in water [19]. Hengquan Yang also prepared a novel catalyst by immobilizing Pd and guanidine on the mesoporous materialSBA-16 via a one-pot silylation and found the catalysts showed better activity for Suzuki coupling and the aerobic oxidation of alcohols [19]. It is concluded modification with support by silylation may improve the property of catalyst and enhance the stability of as-prepared catalysts.

This work aims to prepare a more stable catalyst for CO methanation. By grafting the amino group onto the surface of mesoporous material SBA-16 by silylation and followed the impregnation of Ni, we have successfully synthesized the Ni/SBA-16-NH2 catalysts. The behavior of the prepared catalysts for CO methanation was also investigated and discussed.

Section snippets

Synthesis

SBA-16 was synthesized according to published methods [6], [20]. Typically, 2.5 g Pluronic F127 (Aldrich) and 15 g K2SO4 were dissolved in 150 mL of a 2.0 M HCl aqueous solution. After stirring at 38 °C for 2 h, 12 g tetraethoxysilane (TEOS, Wako, 95%) was then added to this solution. The molar ratio of TEOS/F127/HCl/K2SO4/H2O was controlled at 1/0.0035/1.5/6/166. The obtained mixture was vigorously stirred at 38 °C for 24 h. The mixture is then aged at 100 °C for 24 h under static conditions. The solid

Characterization

FT-IR spectra were recorded on a Nicolet NEXUS 670 FT-IR spectrometer with a DTGS detector, and samples were measured with KBr pellets. Solid-state 29Si magic angle spinning (MAS) NMR spectra were collected on a Varian INOVA 600 MHz instrument. Samples were spun in 3.2 mm zirconia rotors at 7 kHz Typical 29Si MAS NMR parameters were 4000 scans, a 90° pulse length of 5 μs, and a delay of 5 s between scans.

Powder X-ray diffraction (XRD) patterns were recorded on a Bruker advanced D8 powder X-ray

Characterization of the samples

For amino-functionalized materials, it was significant to confirm the success in grafting amino groups the surface and detect the amount of silanol groups available. The FT-IR spectra in Fig.1can provide an evidence for amino functionalization on the SBA-16. For two samples, typical Sisingle bondOsingle bondSi bands of inorganic framework were presented: symmetric vibration around 800 cm-1 and asymmetric stretching vibration around 1089 cm-1. Comparing to SBA-16, SBA-16-NH2 obviously exhibited two additional peaks at

Conclusion

By modification support SBA-16 with silylation, a highly nickel dispersed catalyst was prepared for CO methanation. This catalyst showed high activity for the SNG production with the CO conversion was almost 100% and the CH4 selectivity was 99.9%, respectively. Comparing with the catalyst without modification, a highly dispersion of nickel was found with a much narrow particle size distribution (10 nm). The catalyst could retain the high activity without obvious decline after calcination at 700 

Acknowledgments

This research was financially supported by National Natural Science Funds of China (Grant No. U1203293 and 91434128), the program of Shanghai Subject Chief scientist (Grant No.10Xd1401500) and the Program of Shanghai Leading Talents (2013).

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