Journal of Catalysis 247 (2007) 328–338 www.elsevier.com/locate/jcat Method for the in situ preparation of a single layer of zeolite Beta crystals on a molybdenum substrate for microreactor applications M.J.M. Mies a , E.V. Rebrov a , J.C. Jansen b , M.H.J.M. de Croon a , J.C. Schouten a,∗ a Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands b Catalysis Engineering, DelftChemTech, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands Received 2 October 2006; revised 30 January 2007; accepted 4 February 2007 Abstract A method for the hydrothermal synthesis of a single layer of zeolite Beta crystals on a molybdenum substrate for microreactor applications has been developed. Before the hydrothermal synthesis, the surface of the substrate was modified by an etching procedure that increases the roughness at the nanoscale level without completely eliminating the surface lay structure. Then, thin films of Al 2 O 3 (170 nm) and TiO 2 (50 nm) were successively deposited by atomic layer deposition (ALD) on the substrate. The internal Al 2 O 3 film protects the Mo substrate from oxidation up to 550 ◦ C in an oxidative environment. The high wettability of the external TiO 2 film after UV irradiation increases zeolite nucleation on its surface. The role of the metal precursor (TiCl 4 vs TiI 4 ), deposition temperature (300 vs 500 ◦ C), and film thickness (50 vs 100 nm) was investigated to obtain titania films with the slowest decay in the superhydrophilic behavior after UV irradiation. Zeolite Beta coatings with a Si/Al ratio of 23 were grown at 140 ◦ C for 48 h. After ion exchange with a 10 −4 M cobalt acetate solution, the activity of the coatings was determined in the ammoxidation of ethylene to acetonitrile in a microstructured reactor. A maximum reaction rate of 220 μmol C 2 H 3 Ng −1 s −1 was obtained at 500 ◦ C, with 42% carbon selectivity to acetonitrile.  2007 Elsevier Inc. All rights reserved. Keywords: Zeolite Beta; In situ synthesis; Thin zeolitic coatings; Molybdenum; Atomic layer deposition; Surface roughness; Surface hydrophilicity; Protective coatings; Microreactor; Ethylene ammoxidation; Acetonitrile 1. Introduction Three-dimensional large-pore zeolite Beta (BEA) is cur- rently applied in various catalytic gas- and liquid-phase proces- ses; important examples include the fluid catalytic cracking and dewaxing of petroleum oils [1], alkylation and acyla- tion of aromatics [2,3], isomerization of alkanes [4], Fischer– Tropsch synthesis of iso-paraffins [5], deNOx [6,7], selective hydrogenations [8,9], and ammoxidation of light paraffins and olefins [10]. Besides these large-scale processes, zeolite Beta also is applied in the synthesis of fine chemicals [3]. Extrudates of zeolite Beta, consisting of zeolite crystals and a binder mate- rial, are often applied, resulting in low catalyst efficiency [11]. Application of zeolitic coatings improves catalyst performance, as demonstrated in the case of membrane reactors [12], distilla- * Corresponding author. E-mail address: j.c.schouten@tue.nl (J.C. Schouten). tion units [13], catalytic packings [14,15], monoliths [16], and deNOx reactors [17]. Fast catalytic reactions involving large heat effects can be further intensified when carried out over zeolitic coatings up to 5 μm thick grown directly in the channels of a microstruc- tured reactor, fabricated in a metal substrate [18,19]. The highly exothermic ammoxidation of ethylene to acetonitrile over zeo- lite Beta coatings exemplifies such reactions. The large geo- metrical surface area of the channel walls provides a large interface area between the reactants and the coating. The ab- sence of both binder and macropores improves mass transfer in the coating [11,18]. Heat transfer is enhanced by the chemi- cal bonds between the coating and the substrate, as well as the higher apparent density of the coating [20]. Therefore, methods need to be developed and optimized for the deposition of thin zeolitic coatings on the metal substrate. The hydrothermal syn- thesis method is an elegant way to grow a single layer of zeolite crystals directly in microchannels [18,19,21]. 0021-9517/$ – see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2007.02.007