J. Phys. Chem. C 2007, 111, 17535-17540
17535
Adsorption and Thermal Reaction of Dipropyl Sulfide on Skeletal Ni Adsorbents Xianwen Chu,† Pingjun Guo,† Yan Pei,† Shirun Yan,† Huarong Hu,† Minghua Qiao,*,† Kangnian Fan,*,† Baoning Zong,‡ and Xiaoxin Zhang‡ Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and InnoVatiVe Materials, Fudan UniVersity, Shanghai 200433, People’s Republic of China, and Research Institute of Petroleum Processing, Beijing 100083, People’s Republic of China ReceiVed: February 1, 2007; In Final Form: July 13, 2007
The adsorption and reaction of dipropyl sulfide on Raney Ni and rapidly quenched skeletal Ni (RQ Ni) were studied in ultrahigh vacuum by means of X-ray photoelectron spectroscopy (XPS). Dipropyl sulfide physisorbed on both substrates at 103 K. At 173 K, for Raney Ni, the physisorbed dipropyl sulfide disappeared and the chemisorbed dipropyl sulfide was formed, accompanied by the commencement of C-S bond scission. At the same temperature, for RQ Ni, however, physisorbed dipropyl sulfide was still present, bearing comparable intensity with the chemisorbed dipropyl sulfide, and no atomic S from C-S bond scission was detectable. The lower reactivity of RQ Ni toward dipropyl sulfide is attributed to lattice expansion of the Ni crystallites in RQ Ni posed by rapid quenching. By 473 K, the C 1s peak intensity was totally lost, leaving only atomic S on both substrates. The implication of this work on the regeneration and design of metallic Ni-based adsorbents was addressed.
1. Introduction Organosulfur compounds in fossil-derived transportation fuels constitute a severe problem in our industrial society due to their negative effects on environment and chemical processes.1-3 Because of increasingly stringent environmental regulations, deep desulfurization of transportation fuels is becoming more and more important. The European Union and the United States have planned to reduce sulfur in gasoline and diesel fuel to levels around 10-15 ppmw in the coming years.4-6 Moreover, for proton exchange membrane fuel cells (PEMFCs) using gasoline as feedstock, sulfur content below 0.2 ppmw is preferred.7 It is known that current commercial gasoline usually contains up to 350 ppmw sulfur.6-8 To bridge this huge gap, it becomes imperative to desulfurize the gasoline from the catalytic cracking process (FCC), which is the main body of gasoline and contributes to 80% of sulfur.4 Traditional hydrodesulfurization (HDS) process leads to an unacceptable large drop in octane number due to hydrogenation of olefins, so new technology is required to desulfurize the FCC gasoline.4 Desulfurization by adsorption is a promising method for deep sulfur removal in gasoline under ambient conditions. Zeolites and oxides with or without metal modifications are among the most heavily investigated adsorbents,7,9-14 while only limited attention has been paid to metallic nickel-based adsorbents such as Raney Ni or rapidly quenched skeletal nickel (RQ Ni), which are respectively prepared by alkaline leaching of the naturally and rapidly quenched Ni-Al alloy.15-17 Skeletal Ni has a unique sponge texture and bears the merits of high surface area (ca. 100 m2 g-1), high porosity (ca. 0.1 cm3 g-1), large pore size (ca. 4 nm), low cost, and ready availability,18-21 thus having the potentiality to be a practical desulfurization adsorbent for clean fuel production. Ma et al.15 reported a Ni-based adsorbent * Corresponding authors. Phone: 86-21-55664679. Fax: 86-21-65641740. E-mail:
[email protected] (M.Q.). † Fudan University. ‡ Research Institute of Petroleum Processing.
Ni-Al (A-2) showing high capacity and selectivity for the adsorptive desulfurization of gasoline. Although its exact identity was not given, the A-2 adsorbent is most likely a kind of Raneytype Ni as inferred by its composition and surface area. Lin16 investigated the desulfurization of organosulfur compounds in gasoline over RQ Ni/Ni-M (M ) Mo, Co, Fe, and Cu) adsorbents. The desulfurization efficiency was found to be closely linked to the nature of the organosulfur compounds and the promoters M to the Ni-Al alloy. Jiang et al.17 found that the sulfur level could be reduced to
