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 structured 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 attempted to find an optimized recipe for in situ hydrothermal synthesis of a binderless ZSM-5 coating on stainless steel monoliths with a volume of about 11. Using synthesis mixtures with a typical molar composition of 60 SiO2:Al2O3:4 (TPA)(2)O:4000 H2O, homogeneous zeolitic coatings with an Si/Al ratio of 34 and with coverages of up to 25 g(ZSM-5)/m(packing surface)(2) were obtained in a single synthesis run of 24 h at 150 to 170 degrees C. The coverage increased proportionally with the number of synthesis runs that a packing was subjected to. An effective zeolite density of ca. 200 kg(ZSM-5)/m(packing)(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 significant effect on these figures. By contrast, agitating the synthesis mixture during synthesis proved to be essential to obtain the high coverage values mentioned. (C) 2000 Elsevier Science B.V. All rights reserved.