A comparative study of direct versus post-synthesis alumination of mesoporous FSM-16 silica M. Zimowska a , A. Michalik-Zym a , J. Kry  sciak-Czerwenka a , R. Dula a , R.P. Socha a , K. Pamin a , M. Bazarnik b , K. Bahranowski c , Z. Olejniczak d , L. Lity  nska-Dobrzy  nska e , E.M. Serwicka a, * a Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Krakow, Poland b Cracow University of Technology, Faculty of Civil Engineering, ul. Warszawska 24, 31-155 Krakow, Poland c Faculty of Geology, Geophysics and Environmental Protection, AGH-University of Science and Technology, al. Mickiewicza 30, 30-059 Krakow, Poland d Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, 31-342 Krakow, Poland e Institute of Metallurgy and Material Chemistry, Polish Academy of Sciences, ul. Reymonta 9, 30-059 Krakow, Poland A R T I C L E I N F O Article history: Received 21 April 2016 Received in revised form 24 June 2016 Accepted 13 July 2016 Available online 15 July 2016 Keywords: FSM-16 Mesoporous silica Alumination Al distribution Acidity A B S T R A C T Al-FSM-16 mesoporous silicas were synthesized either by direct method, from Al-kanemite (Al-FSM-16/ D), or by post-synthesis impregnation of purely siliceous FSM-16 with Al(NO 3 ) 3 (Al-FSM-16/P) and characterized with XRD, XRF, SEM, TEM, nitrogen sorption isotherms, 27 Al and 29 Si MAS NMR, FTIR, XPS, NH 3 -TPD, FTIR of pyridine adsorption and catalytic decomposition of ethanol. Only substitutional Al sites exist in Al-FSM-16/D, while in Al-FSM-16/P some Al remains in extra-lattice positions. Upon transformation of Al-FSM-16/D into hydrogen form a certain amount of extra-framework Al is formed. Direct alumination introduces a higher degree of structural disorder. In Al-FSM-16/D, Al is preferentially accumulated at inner pore walls, while in Al-FSM-16/P external surface is Al-rich. Post-synthesis alumination is more efficient in introducing acid sites into FSM-16. The generated acidity is of Brønsted and Lewis nature, the latter being stronger than the former. ã 2016 Elsevier Ltd. All rights reserved. 1. Introduction Ordered mesoporous silicas represent an important class of porous structures with well defined pores of controlled dimen- sions, shape and connectivity. The materials find many applica- tions, particularly in the field of catalysis, separation processes, and host-guest chemistry. Alumination of the mesoporous silicas is one of the most popular method of their modification. Isomorphous substitution of Al for Si aims at development of cation exchange/ acid properties, and extends further potential of these materials as hosts, adsorbents or catalysts. Formation of Al-containing ordered mesoporous silica frameworks had already been described in the 1992 reports on the syntheses of MCM-41 [1], and the material referred to later as FSM-16 [2]. FSM-16 silicas, derived from kanemite, a layered sodium silicate of the formula NaHSi 2 O 5  3 H 2 O, are structurally analogous to the extensively studied MCM-41 materials, as they are highly ordered mesoporous solids with a hexagonal array of uniform channels, high specific surface area and pore volume [3]. Insertion of aluminum into mesoporous silicas is usually carried out by one of the two well established synthesis routes: direct method, consisting in addition of Al source to the synthesis gel, or post-synthesis treatment, in which Al source is incorporated into purely siliceous mesoporous framework by such means as grafting or impregnation. The literature on MCM-41 alumination by either of the procedures is plentiful [1,2,4–32], and includes many studies comparing the effects of direct versus post-synthesis alumination [20–32]. It has been shown that the method of Al insertion determines the material structure, stability, Al distribution, acidity and catalytic properties. In contrast to copious findings related to MCM-41 aluminosi- licates, the reports investigating the effect of alumination on FSM- 16 structure and properties are much fewer [2,33–39]. It should be noted, that despite close structural similarities between MCM-41 and FSM-16, the materials are formed via essentially different mechanisms [40–42]. The cooperative self-assembly of surfactant and a dissolved silica source, operating during the synthesis of MCM-41, leads to a direct build up of the hexagonal mesophase * Corresponding author. E-mail address: ncserwic@cyf-kr.edu.pl (E.M. Serwicka). http://dx.doi.org/10.1016/j.materresbull.2016.07.016 0025-5408/ã 2016 Elsevier Ltd. All rights reserved. Materials Research Bulletin 83 (2016) 623–631 Contents lists available at ScienceDirect Materials Research Bulletin journal homepage: www.else vie r.com/locat e/mat resbu