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Supported cobalt catalysts are the catalysts of choice for synthesis of paraffinic hydrocarbons from carbon monoxide and hydrogen. In this paper, the number and intrinsic activity of cobalt nanoparticles promoted with Pt localized in zeolites with different structures and pore diameters (ZSM-5, MOR and BEA) have been investigated by steady state isotopic kinetic analysis (SSITKA) under conditions favouring higher methane selectivity. Promotion with Pt resulted in a higher number and higher reactivity of surface intermediates leading to methane. The cobalt catalyst supported by MOR zeolite displayed the highest SSITKA reaction rate in carbon monoxide hydrogenation, followed by Co supported on BEA and then Co supported on the zeolite ZSM-5. Good dispersion of cobalt nanoparticles inside and outside the surface of the MOR and BEA zeolites led to a higher number of active sites. On the other hand, poor dispersion of cobalt nanoparticles on the external surface of ZSM-5 resulted in the lowest intrinsic catalytic activity and lowest number of active sites. The intrinsic activity of cobalt sites was, however, almost unaffected by the inclusion of cobalt nanoparticles in the zeolite pores.

A new strategy for the synthesis of metal–zeolite nanocomposite materials containing metal nanoparticles only in the zeolite pores is proposed. These materials were first prepared by zeolite impregnation with metal salts which resulted in metal species located both inside the zeolite pores and on the zeolite outer surface. Then, the metal oxide nanoparticles on the external zeolite surface were selectively extracted by larger heteropolyacid molecules which cannot enter the zeolite pores. The use of cobalt–zeolite nanocomposites with cobalt nanoparticles selectively encapsulated in the zeolite pores led to significantly higher selectivity to C5–C12branched hydrocarbons in Fischer–Tropsch synthesis with the maximum ratio of isoparaffins to n-paraffins of 5.8.

Zeolite membranes stand out for presenting molecular sized uniform pores. The current work aimed to optimize supported template-free ZSM-5 zeolite membrane preparation by evaluating the effect of two parameters: successive synthesis cycles of the zeolitic film and aging time of the synthesis solution. The zeolitic film synthesis was carried out by secondary hydrothermal treatment using α-alumina tubes as support, commercial zeolite as seeds and SiO2: 0.3 Na2O: 0.01 Al2O3: 114 H2O as molar composition of the synthesis solution. The aging time tested for the dissolution of silicon and aluminum was 30, 60, 120 or 180 ​min; whilst for the silicon and aluminum mix was 60 or 15 ​min. Hydrothermal synthesis was performed at 180 ​°C for 24 ​h. This procedure was executed 1, 2 or 4 times. One synthesis cycle was already capable of producing a homogeneous zeolitic film on the support with crystal interconnection. This finding was corroborated by gas permeation tests, in which the membrane did not show any apparent defects. The aging time had an effect on the type of zeolite formed. Only the aging time conditions of 180 and 60 ​min and 180 and 15 ​min prompted the exclusive formation of zeolite ZSM-5.