Anti‐Coke Properties of Acid‐Treated Bentonite‐Supported Nickel‐Boron Catalyst

Abstract

Boron was introduced into nickel/acid-treated bentonite (Ni/A-Bn) catalysts to improve the anti-coking ability of the nickel-based catalyst in the hydrogenation of nitrobenzene. The results showed the B-doped Ni/A-Bn catalyst was more active than that without B. During an extended reaction period, Ni-B/acid-treated bentonite (Ni-B/A-Bn) resulted in a high nitrobenzene conversion and a high aniline selectivity. The lifetime of Ni-B/A-Bn was extended significantly compared with that of Ni/A-Bn. The addition of B into Ni/A-Bn decreased the NiO particle size, improved the dispersion of active components, and decreased carbon deposition. The combination of B and Ni prevented coke deposition on metallic Ni during nitrobenzene hydrogenation, which reduced carbon deposition on the surface of Ni-B/A-Bn. IntroductionAniline is an important chemical in industry [1,2], and is mainly produced by phenol ammonization, iron powder reduction, and catalytic hydrogenation of nitrobenzene. Among these methods, catalytic hydrogenation does not generate acid effluents and has little impact on the environment, compared with the other two methods. Catalytic hydrogenation of nitrobenzene in a gas-liquid-solid system, which is a greener method, is the main way to obtain aniline in very high yields [3][4][5]. A noble metal is commonly used in catalytic reaction due to excellent catalytic activity and higher coking resistance [6][7][8][9][10]; however, the cost is too high and limits industrial applications. As a transition metal, nickel-based catalysts exhibit high activity for hydrogenation and are low-cost compared with noblemetal-based catalysts [11]. In industry, nickel-based catalysts are generally used in the form of Raney Ni; however, this is easily deactivated by sintering. Additionally, catalyst deactivation is also caused by carbon deposition, which a general problem for hydrogenation [12,13]. Many studies of carbon chemisorption on Ni surfaces have further refined understanding of the molecular-level behavior of carbon atom deposition on Nibased catalysts [14][15][16], and it has been suggested that a small amount of boron could enhance the stability of Ni-based catalysts [15,16]. The atomic number of boron close to that of carbon, and shows similar chemisorption preferences on Ni-based catalysts; therefore, a small amount of boron might block most of the stable binding sites. Furthermore, calculations have demonstrated that these sites probably initiate coke formation [14,15] or lead to low catalytic activity when covered by carbon atoms [16]. Initial studies indicated that blocking by boron potentially reduced deactivation, and boron could influence the coking resistance of nickel-based catalysts during the steam reforming of methane [17].Bentonite is a good catalyst support due to its strong metalsupport interaction and low cost. Coking on the Ni surface is a technological problem and has been addressed in many studies [18][19][20][21][22]. Ni/bentonite was used as a catalyst for nitrobenzene hydrogenation to form aniline; ...

Mn Modified Ni/Bentonite for CO2 Methanation

“…Among them, transition metal Mn exhibited the properties of the adjusted d-electron structure and could improve the surface area of the active metal, as well as the metal dispersion on the support [30]. In the present study, to improve the catalytic activities and stabilities of the Ni/bentonite catalysts, based on the previous research about the Ni-based catalysts [25,31,32], Mn was used to modify the Ni/bentonite prepared by SCS using urea as a fuel, and was applied in the CO 2 catalytic hydrogenation to CH 4 . Furthermore, the Ni/bentonite catalysts were characterized by X-ray diffraction (XRD), H 2 temperature-programmed reduction (H 2 -TPR), scanning electron microscope (SEM), N 2 -adsorption/desorption, and X-ray photoelectron spectroscopy (XPS).…”