Short Communication Effects of potassium doping on CO hydrogenation over MoS 2 catalysts: A first-principles investigation Amity Andersen a , Shawn M. Kathmann b , Michael A. Lilga c , Karl O. Albrecht c , Richard T. Hallen c , Donghai Mei b, ⁎ a Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, USA b Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA c Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA abstract article info Article history: Received 3 December 2013 Received in revised form 3 February 2014 Accepted 12 February 2014 Available online xxxx Keywords: CO hydrogenation MoS 2 catalyst Alkali metal Promotion Density functional theory The effects of potassium (K) doping on the reactivity of CO hydrogenation over MoS 2 (100) catalysts are investigated using periodic density functional theory (DFT) calculations. The surface doped K species enhances the CO adsorption by providing both K\O and K\C bonding. DFT results show that K-doping promotes the C\C coupling step forming the H 2 CCO precursor that leads to the formation of mixed higher C 2+ oxygenates. Different reaction routes for CO hydrogenation on the Mo and the S edges over MoS 2 (100) catalysts are identified. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Catalytic conversion of biomass-derived syngas (CO/CO 2 /H 2 O) to mixed higher (C 2+ ) alcohols has attracted tremendous interests in both academia and industries [1,2]. Currently, fast methanation and slow kinetics of the initial C\C coupling formation that lead to low alco- hol yields and poor selectivity are two major hurdles for the commer- cialization of syngas conversion to the C 2+ alcohols. With its unique chemical and physical nature such as sulfur-resistance and slow coking deactivation, MoS 2 based catalysts have been shown as the promising catalyst for the C 2+ alcohol selectivity by adding alkali metal promoters [2]. Christensen et al. found that with more than 103 ppmv H 2 S in the reactant feed the mixed C 2+ alcohols instead of methanol became the dominant products using K 2 CO 3 /Co/MoS 2 /C catalysts [3]. The promoting effects of metal alkali species on the selectivity of syngas conversion are assumed to be two-fold. On one hand, the addition of basic alkali promoters will neutralize the surface acidity, thus suppressing various side reactions such as isomerization, dehydrogenation and coking. On the other hand, the alkali promoters can reduce the active sites for CO dissociation that are responsible for hydrocarbon formation. Lee et al. suggested that the addition of a limited amount of potassium ion (K + ) promoters modifies the interaction of CO and the MoS 2 surface [4]. Iranmahboob et al. also reported that the K-promoted MoS 2 catalyst is more active and selective for higher alcohol synthesis than the Cs- promoted MoS 2 catalyst [5,6]. Although extensive experimental studies have been performed as mentioned above, the reaction mechanisms of CO hydrogenation to the C 2+ alcohols (or more generally C 2+ oxygen- ates) are far from being fully understood. Li et al. proposed a reaction mechanism on the transition metal (Fe, Co or Ni) promoted MoS 2 - based catalyst [7]. Two catalytic phases (MS x and M-KMoS) with differ- ent reaction pathways were suggested. CO dissociates and is further hydrogenated into CH x and methane on the MS x phase while the non- dissociative adsorbed CO on the mixed M-KMoS phase inserts into a metal–methyl carbon bond producing an oxygenate precursor, which upon further hydrogenation or dehydration forms mixed C 2+ oxygen- ates and hydrocarbons. The CO hydrogenation mechanism is further complicated with varying surface compositions and structures on the MoS 2 catalyst. The exposed active surface sites of the MoS 2 catalyst change with reaction conditions, ranging from the full Mo-terminated, to the partial S-terminated and to the full S-terminated surface. Previous theoretical calculations suggested that the full Mo-terminated or full S-terminated MoS 2 surface is not stable under the pressure ratio P H2S /P H2 between 10 -4 and 10 4 [8]. The most stable MoS 2 surface structure, i.e. MoS 2 (10-10), is terminated by Mo metal sheets covered with 50% S coverage or S sheets with 50% S vacancies on the surface. Shi et al. studied CO hydrogenation on these two MoS 2 (10-10) surfaces using density functional theory (DFT) calculations [9]. They found that the CO hydrogenation route is as follows: CO → þH HCO → þH H2CO → þH H2COH → -OH CH2 → þH CH3 → þH CH4. Catalysis Communications xxx (2014) xxx–xxx ⁎ Corresponding author. E-mail address: donghai.mei@pnnl.gov (D. Mei). CATCOM-03814; No of Pages 6 http://dx.doi.org/10.1016/j.catcom.2014.02.011 1566-7367/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom Please cite this article as: A. Andersen, et al., Effects of potassium doping on CO hydrogenation over MoS 2 catalysts: A first-principles investigation, Catal. Commun. (2014), http://dx.doi.org/10.1016/j.catcom.2014.02.011