Hydrodesulfurization of 4,6-dimethyldibenzothiophene and its hydrogenated intermediates over bulk Ni 2 P Lei Yang a , Xiang Li a,b,c,⇑ , Anjie Wang a,b,c , Roel Prins d , Yao Wang b,c , Yongying Chen a,b , Xinping Duan a,e a State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, No. 2 Linggong Road, Dalian 116024, PR China b Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, No. 2 Linggong Road, Dalian 116024, PR China c Penn State and Dalian University of Technology, Joint Center for Energy Research (JCER), Dalian University of Technology, No. 2 Linggong Road, Dalian 116024, PR China d Institute of Chemical and Bioengineering, ETH Zurich, 8093 Zurich, Switzerland e Department of Chemistry, National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters, Xiamen University, Xiamen 361005, PR China article info Article history: Received 8 April 2014 Revised 12 June 2014 Accepted 16 June 2014 Keywords: Hydrodesulfurization 4,6-Dimethyldibenzothiophene Hydrogenated intermediates Nickel phosphide Piperidine abstract The hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and its hydrogenated intermediates 1,2,3,4-tetrahydro-4,6-dimethyldibenzothiophene (TH-4,6-DMDBT) and 1,2,3,4,4a,9b- hexahydro-4,6-dimethyldibenzothiophene (HH-4,6-DMDBT) over a bulk Ni 2 P catalyst was studied at 340 °C and 4.0 MPa in the presence and absence of piperidine. The rate constants of all steps in the net- work of the HDS of 4,6-DMDBT were measured. The HDS of 4,6-DMDBT occurred predominantly through the hydrogenation (HYD) pathway, and the HYD and direct desulfurization pathways were about equally inhibited by piperidine. Piperidine inhibited the desulfurization of TH-4,6-DMDBT and 4,6-DMDBT in the same way, but did not affect that of HH-4,6-DMDBT. In contrast to the HDS of TH-4,6-DMDBT over metal sulfide catalysts and to the HDS of TH-DBT, a fast dehydrogenation of TH-4,6-DMDBT to 4,6-DMDBT was observed. Besides 4,6-DMDBT, a small amount of the methyl-migration isomers was detected in the dehydrogenation product of TH-4,6-DMDBT, which is ascribed to the metallic character of Ni 2 P. Ó 2014 Elsevier Inc. All rights reserved. 1. Introduction Deep desulfurization has become ever more important because of the need to process lower quality crude oil feed stocks contain- ing high sulfur levels and the increasing restrictions on sulfur contents of transportation fuels. In a modern refinery, the sulfur- containing compounds in liquid fuels are removed mainly via the hydrodesulfurization (HDS) process. Dibenzothiophene (DBT) and its alkylated derivatives such as 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene (4,6-DMDBT) are the most refrac- tory sulfur-containing molecules to hydrodesulfurize [1]. The HDS reaction networks of these molecules are complex and can be divided into two parallel pathways: direct desulfurization (DDS) and hydrogenation (HYD). DDS leads to the formation of biphenyls, while HYD yields not only the final desulfurized prod- ucts such as cyclohexylbenzenes and bicyclohexyls, but also the tetrahydro (TH), hexahydro (HH), and dodecahydro (DH) sulfur- containing intermediates [2]. Therefore, the HDS reactions of both the parent molecules and their hydrogenated intermediates should be investigated to gain sufficient information on the removal of the sulfur atoms from these sulfur-containing compounds. This is par- ticularly important for 4,6-DMDBT because the DDS pathway is less important for the HDS of 4,6-DMDBT than the hydrogenation pathway [3,4]. Egorova and Prins studied the HDS of DBT and 4,6-DMDBT over sulfided NiMo/c-Al 2 O 3 , CoMo/c-Al 2 O 3 , and Mo/ c-Al 2 O 3 catalysts at 340 °C and a total pressure of 5 MPa [2]. They reported that over the CoMo/c-Al 2 O 3 catalyst, the selectivity of biphenyl (the product of the DDS of DBT) was 70%, while the selec- tivity toward the formation of 3,3 0 -dimethylbiphenyl (DM-BP, the product of the DDS of 4,6-DMDBT) was only 12%. The low DDS reactivity of 4,6-DMDBT is due to the steric hindrance of the methyl groups at the 4 and 6 positions, which are close to the sul- fur atom and prevent the r-binding of the sulfur atom with the catalytic site [5,6]. Transition-metal phosphides (e.g., WP, MoP, Co 2 P, CoP, Ni 2 P) are a family of promising hydrotreating catalysts [7–14]. Among the phosphides, Ni 2 P exhibited an excellent activity in hydroprocess- ing [15,16]. The overall activity of the transition-metal phosphides in the simultaneous HDS of DBT and hydrodenitrogenation (HDN) of quinoline was in the order Fe 2 P < CoP < MoP < WP < Ni 2 P [8,17]. For the development of high-performance transition-metal phosphide HDS catalysts, an intensive study of the HDS reaction http://dx.doi.org/10.1016/j.jcat.2014.06.020 0021-9517/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author at: School of Chemical Engineering, Dalian University of Technology, Dalian 116024, PR China. Fax: +86 411 84986121. E-mail address: lixiang@dlut.edu.cn (X. Li). Journal of Catalysis 317 (2014) 144–152 Contents lists available at ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat