Higher Alcohols through CO Hydrogenation over CoCu Catalysts: Inﬂuence of Precursor Activation Yizhi Xiang, †,‡ Roland Barbosa, †,‡ and Norbert Kruse* ,†,‡ † Chemical Physics of Materials (Catalysis-Tribology), Universite ́ Libre de Bruxelles, Campus Plaine, CP 243, 1050 Brussels, Belgium ‡ Catalysis for Clean Energy and Environment, Voiland School of Chemical Engineering and Bioengineering, Washington State University, P.O. Box 646515, Pullman, Washington 99164-6515, United States * S Supporting Information ABSTRACT: Bimetallic CoCu model catalysts were investigated for the synthesis of higher alcohols using catalytic CO hydrogenation according to the Fischer-Tropsch technology. Emphasis was placed on revealing the inﬂuence of the activation conditions. Accordingly, catalyst precursors were activated in argon, hydrogen, syngas (CO/H 2 ), and CO under atmospheric conditions and at elevated temperatures (370 °C). All catalyst precursors were prepared via oxalate coprecipitation in the absence of a classic support. Alcohol selectivities between 30 and ∼40% (up to ∼50% for the sum of alcohols and alkenes) were obtained with an Anderson-Schulz-Flory (ASF) chain lengthening probability maximizing the slate up to C 6 . Detailed catalysis and characterization studies were performed using a Co 2 Cu 1 catalyst composition. The catalytic perform- ances of the H 2 - and syngas-activated Co 2 Cu 1 catalyst were similar. While the CO-activated catalyst shows signiﬁcantly higher catalytic activity and ASF chain lengthening probability, the alcohol selectivities are lower than those of H 2 - or syngas-activated ones. All catalysts required time on stream for several hours to achieve steady-state catalytic performance. Co 2 Cu 1 catalysts were characterized by temperature-programmed decomposition (TPDec), in situ N 2 physisorption (Brunauer-Emmett-Teller), transmission electron microscopy (TEM), and in situ X-ray photoelectron spectroscopy (XPS). The data indicate major restructuring occurs during activation. An “onion-like” graphitic carbon shell was observed via TEM for the CO-activated Co 2 Cu 1 catalyst, which probably originated mainly from the Boudouard reaction (2CO + [] ad → C ad + CO 2 ). This interpretation is in accordance with the TPDec proﬁles and XPS results. The latter also indicates that syngas and CO activation lead to higher than nominal Co/Cu surface ratios. The surface segregation of Co in the presence of CO atmospheres is interpreted on the basis of Co@Cu core-shell structured particles. KEYWORDS: CoCu catalysts, oxalates, thermal decomposition, CO hydrogenation, higher terminal alcohols ■ INTRODUCTION Terminal C 2+ alcohols play an important role as fuel additives and provide the feedstock for plasticizers, detergents, and lubricants. Traditionally, such alcohols are synthesized through hydroformylation of a C n (n ≥ 3) 1-alkene and subsequent hydrogenation of the C n+1 aldehydes. Alternative synthetic procedures have been developed more recently as, for example, anti-Markovnikov 1-alkene hydration 1 and one-pot hydro- formylation/hydrogenation 2 using homogeneous catalysis. Given the continuing problems in complying with the Markovnikov rule and recovering the noble metals from the homogeneous process, direct CO hydrogenation according to the heterogeneous Fischer-Tropsch (FT) technology may be considered a viable and promising alternative for the future. 3 The possibility of changing the selectivity of the FT synthesis from hydrocarbons to alcohols consists of replacing Co-based catalysts by bimetallic Co-Cu-based ones. First attempts with the latter were reported by the Institut Francais du Petrole (IFP) in the late 1970s. 4 The focus at that time was on the selective production of C 2 -C 6 iso- and n-alcohols as fuel additives using CO/CO 2 -H 2 feeds in an operating manner similar to the industrial methanol synthesis. Most of the present-day studies with such catalysts are aimed at further improving the performance of short chain alcohol synthesis. 4,5 More recently, it was demonstrated that Co-Cu bimetallic catalysts can be tuned for the selective formation of long chain C 8 -C 14 terminal alcohols using ternary Co-Cu-Mn and Co- Cu-Mo catalysts. 6 Co-Cu-Mn catalysts, prepared by oxalate coprecipitation of the three metals, were shown to exhibit core@shell structured metal nanoparticles, with Co forming the core and all three elements being present in an otherwise Cu- dominated shell with a thickness of ∼2 nm. 6 Moreover, metal oxide particles were identiﬁed, with Mn 5 O 8 forming the most signiﬁcant oxidic phase. In this work, we focus on binary “CoCu” systems for which phase-separated single metal oxides are much less abundant or even absent. Similar to ternary Received: May 21, 2014 Revised: July 11, 2014 Published: July 14, 2014 Research Article pubs.acs.org/acscatalysis © 2014 American Chemical Society 2792 dx.doi.org/10.1021/cs500696z | ACS Catal. 2014, 4, 2792-2800