Applied Surface Science 351 (2015) 250–259 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Surface chemistry and catalytic performance of chromia/alumina catalysts derived from different potassium impregnation sequences Daolan Liu a , Peng Bai a,∗ , Pingping Wu a , Dezhi Han b , Yongming Chai a , Zifeng Yan a,∗ a State Key Laboratory of Heavy Oil Processing, PetroChina Key Laboratory of Catalysis, School of Chemical Engineering, China University of Petroleum, Qingdao 266580, PR China b Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Science, Qingdao 266101, PR China a r t i c l e i n f o Article history: Received 11 March 2015 Received in revised form 18 May 2015 Accepted 21 May 2015 Available online 29 May 2015 Keywords: Impregnation sequences Chromium catalysts Potassium Propane dehydrogenation a b s t r a c t Chromia/alumina catalysts prepared with different K impregnation sequences were compared in the dehydrogenation of propane. The materials were characterized by a variety of techniques. The catalyst with K impregnated prior to Cr loading (sample Cr/K/Al 2 O 3 ) exhibited higher propene selectivity than that prepared with the reverse impregnation sequence (sample K/Cr/Al 2 O 3 ). Catalyst Cr/K/Al 2 O 3 possesses a higher amount of surface acid sites and more readily reducible chromium species compared with catalyst K/Cr/Al 2 O 3 . The majority of chromium species were observed to exist as polymeric species on catalyst Cr/K/Al 2 O 3 , while isolated and oligomeric chromium species were mainly found on catalyst K/Cr/Al 2 O 3 . A detailed correlation between catalytic performance and characterization results demonstrated that isolated and oligomeric species possessed higher cracking and coking activities than polymeric chromium species, which may account for the difference in the propene selectivity of catalysts. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Technologies for propane dehydrogenation have attracted extensive attention due to the increasing demand for propene, an important intermediate feedstock for various chemicals, such as polypropylene, propylene oxide, polyacrylonitrile, cumene, acrolein, and acrylic acid. There are mainly two approaches to the catalytic dehydrogenation of propane: oxidative and non-oxidative dehydrogenation. For the oxidative dehydrogenation, there are no constrains of thermodynamic equilibrium in theory and the reaction temperature is lower in comparison with non-oxidative dehydrogenation. However, serious problems associated with deep oxidation, low selectivity, heat removal, and safety issues exist in the processes with O 2 or CO 2 as oxidants, impeding the commer- cialization of oxidative dehydrogenation technologies [1,2]. By contrast, the non-oxidative catalytic dehydrogenation of propane has been successfully commercialized. Platinum-based and chromium-based catalysts are commonly applied in com- mercial catalytic dehydrogenation processes. Due to the low cost and excellent catalytic performance, chromium catalysts have drawn extensive attention both in academia and in industry [3–7]. ∗ Corresponding authors. Tel.: +86 532 86981856; fax: +86 532 86981295. E-mail addresses: baipeng@upc.edu.cn, superbaipeng@126.com (P. Bai), zfyancat@upc.edu.cn (Z. Yan). However, pristine chromium catalysts usually deactivate fast and have a low selectivity towards propene due to the high cracking and coking activities, requiring modification by adding promoters. Potassium is a widely used promoter in chromium catalyst mod- ification. It may improve or suppress activity and selectivity of catalyst, depending on the amount of potassium added [8]. It is generally recognized that the addition of potassium neutralizes surface acidity of both alumina and chromia, which is crucial to achieve a satisfactory dehydrogenation performance. As a matter of fact, the surface acidity of catalysts for propane dehydrogenation can be neither too high which will cause the decrease of propene selectivity, nor too low which will lead to the lack of initial activity [8]. The potassium amount was found to affect the acid strength distribution and weak and medium acid sites were observed to be preferentially neutralized at K loadings of above 0.5 wt.% [8]. Besides the surface acidity properties, the distribution of chromium species and correspondingly the reducibility of catalysts were also reported to be influenced by potassium addition amount [9]. With potassium content increasing, the Cr 6+ content was reported to increase and that of Cr 3+ which was considered to be the active species [7,10], remained almost the same or decreased slightly, resulting in the increase of the Cr 6+ /Cr 3+ ratio. Given that the surface chemistry of chromia/alumina catalysts is sensitive to the addition amount of K, a question arises reasonably whether the potassium addition way, for instance, the potassium addition sequence matters. Unfortunately, so far, there is no report http://dx.doi.org/10.1016/j.apsusc.2015.05.128 0169-4332/© 2015 Elsevier B.V. All rights reserved.