Amorphous silica-alumina matrix

The Plank group was large and emphasized preparation and activity testing of an enormous number of zeolite catalysts. They soon Incorporated a zeolite in an amorphous silica-alumina matrix and found that the initial activity of this catalyst was vastly superior to any amorphous silica-alumina catalyst that was utilized at that time. With this encouraging result, they quickly improved upon their catalyst formulation and a number of patents were obtained. They obtained a synergetic effect with their catalysts since they had superior activity and selectivity over that expected from the sum of the two when tested separately. 

Most of the studies on plastic and rubber hydrogenation are based on the use of catalysts to promote cracking and hydrogenation reactions. A wide variety of catalysts have been examined, consisting typically of transition metal compounds (Fe, Mo, Ni, Co, etc.) supported on an acid porous matrix (alumina, amorphous silica-alumina, zeolites, sulfated zirconia, etc.). 

The precursor of a similar fiber was prepared by polycondensation of an organoaluminum compound, such as monoisopropoxydiethyl aluminum, dissolved in ethylether [60]. Some isopropoxy groups were presumably replaced by a phenoxy group, such as ethyl 0-hydroxybenzoate, in order to improve the spinnability of the final dope. The polyaluminoxane was dissolved in benzene, the ether was distilled off and ethyl silicate was added. After concentration, the dope was dry spun and the green fibers were aged in a humid atmosphere and calcined. The fibers (Table II) had a glassy appearance and were composed of a nanocrystalline Al-Si spinel phase (or r /y-transition alumina) in an amorphous silica based matrix [33] [53]. After mullitization that starts at 1150 C and is complete after 2 min at 1400 C, the fibers were composed of mullite and corundum [33]. 

Table III compares the gasoline composition from three steam deactivated catalyst systems. The first contains 10% rare earth exchanged faujasite (RE FAU) in an inert silica/clay matrix at a cell size of 2.446 nm the second contains 20% of an ultra stable faujasite (Z-14 USY) at a unit cell size of 2.426 nm in inert matrix. The third contains 50% amorphous high surface area silica-alumina (70% AI2O3 30% Si02) and 50% clay the nitrogen BET surface area of this catalyst after steam deactivation is 140 m /g. All three catalysts were deactivated for 4 hrs. at 100% steam and at 816°C.

Hydrocracking Pd on zeolite in an amorphous matrix NiMo on silica-alumina, various other dual-function catalysts (adiabatic fixed beds)... 

The introduction of zeolites in cracking catalysts combined with various non-zeolite matrix types (a.o. higher stability silica-alumina types) certainly complicates the picture of FCC hydrothermal deactivation. Letzsch et al [7] have shown that like amorphous catalysts the zeolite is more strongly deactivated hydrothermally than purely thermally. 

Carbon molecular sieves, or carbogoric sieves are amorphous materials made by pyrolyz-ing coal, coconut shells, pitch, phenol-formaldehyde resin, or other polymers. EKslocations of aromatic microdomains in a glassy matrix give their porosity. Pores are slit-shaped. Pore structure is controlled by the temperature of the pyrolysis. Pore widths range from 3 A to 10 A. Acarbogenic sieve made from polyfurfuryl alcohol and combined with silica-alumina was selective for monomethylamine production from methanol and ammonia [54]. 

The catalysts used for cracking before the 1960s were amorphous [Si-Al] catalysts. The replacement of these catalysts by faujasite zeolites was a big step forward in the oil refining industry, which led to an increase in the production of gasoline [20], The acid catalyst, currently used in FCC units, is generally composed of 5-40 wt % of 1-5 pm crystals of the H-Y zeolite included in a porous particle composed of an active matrix, which in turn is composed of amorphous alumina, silica, or [Si-Al] and a binder. The porous particle allows the diffusion of the reactants and products of the cracking reaction to and from the micropores of the zeolite [10]. 

Whereas the majority of experimental works has been focused on silica-, glass-or alumina-embedded noble metal nanoparticles, or aqueous colloidal solutions, a few ones have dealt with other kinds of matrices, either amorphous (BaO [177], BaTiOj [164, 167], Bi.()., [178], Nb.O, [179], TiO. [180, 181], ZrO. .. [167]) or crystalline (BaTiOj [164, 182, 183], BiT) [184], LiNbOj [185], SrTiOj [172], ZnO... [186]). A direct comparison of the nonlinear properties from one matrix to another is difficult to carry out, since all other parameters should be kept constant while tuning the wavelength as to match the SPR maximum. 

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