Optimization of the preparation of binderless ZSM-5 coatings on stainless steel monoliths by in situ hydrothermal synthesis

Metal monoliths containing binderless zeolitic coatings are interesting str uctured catalyst packings that combine attractive hydrodynamical properties , such as a low pressure drop, with special chemical properties, such as a high catalyst effectiveness and a high reaction selectivity. It was attempt ed to find an optimized recipe for in situ hydrothermal synthesis of a bind erless ZSM-5 coating on stainless steel monoliths with a volume of about 11 . Using synthesis mixtures with a typical molar composition of 60 SiO2:Al2O 3:4 (TPA)(2)O:4000 H2O, homogeneous zeolitic coatings with an Si/Al ratio o f 34 and with coverages of up to 25 g(ZSM-5)/m(packing surface)(2) were obt ained in a single synthesis run of 24 h at 150 to 170 degrees C. The covera ge increased proportionally with the number of synthesis runs that a packin g was subjected to. An effective zeolite density of ca. 200 kg(ZSM-5)/m(pac king)(3) was obtained in a sequence of four runs. Neither the state of the silicon source (TEOS or colloidal silica) nor the curvature of the support surface (monoliths constructed from foil or 35 mu m wire gauze) had a signi ficant effect on these figures. By contrast, agitating the synthesis mixtur e during synthesis proved to be essential to obtain the high coverage value s mentioned. (C) 2000 Elsevier Science B.V. All rights reserved.