Iron-containing molecular sieves, synthesi

The subsequent Chapter 7 is devoted to the synthesis and characterization of molecular sieve materials containing transition metals in the framework. Authored by G. Perego, R. Millini and G. Bdlussi, this Chapter focuses on titanium-silicalite-1 which has recently been found to be a unique catalyst for selective oxidations with hydrogen peroxide. Also covered in this Chapter is the synthesis of vanadium- and iron-containing molecular sieves. 

As for Ti- and V-containing molecular sieves, the synthesis conditions must assure the suppression of the polymerization/precipitation reactions of iron oxide/hydroxide species. Though the aquo-chemistry of Fe + is well documented (see [133] and references therein), little information is available on the behavior of Fe sources in the presence of silica, particularly under the hydrothermal conditions necessary for the crystallization of molecular sieves. Monomeric octahedral aquo-hydroxocomplexes of iron are stable only at pFl < 2. At higher... 

Oxygen-containing molecules cannot be tolerated in the ammonia synthesis, primarily because they form iron oxide that blocks the active surface. First the CO2 is removed, through a scrubber, by reaction with a strong base. The remaining CO (and CO2) is then removed by the methanation reaction, converting the CO into methane and water. Finally the water is removed by, for example, molecular sieves. Methane does not present problems because it interacts weakly with the catalyst surface. The gas mixture (Tab. 8.6) is compressed to the roughly 200 bar needed for ammonia synthesis and admitted to the reactor. 

The desire to synthesize molecular sieve compositions containing other than the typical silicon and aluminum atoms is evidenced by the large number of efforts, primarily in the primary synthesis area. The Secondary Synthesis process has now been extended to include substitution of both Fe3t and T1 + into the frameworks of a number of zeolites. This paper will describe substitution of iron or titanium ions into the frameworks of zeolites Y, L, W, mordenite, ZSM-5 and LZ-202. Zeolites Y, L, W and mordenite were obtained from Union Carbide Corporation. Zeolon, a synthetic mordenite, was obtained from The Norton Company. ZSM-5 was synthesized according to the procedures described by Argauer et al., (8). LZ-202 is an omega type zeolite, synthesized without the... 

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