Zeolite activation

Cracking, a rupturing of carbon-carbon bonds—for example, of gas oils to gasohne—is favored by sihca-alumina, zeolites, and acid types generally. Zeohtes have pores with small and narrow size distribution. They crack only molecules small enough to enter the pores. To restrain the undesirable formation of carbon and C3-C4 hydrocarbons, zeolite activity is reduced by dilution to 10 to 15 percent in silica-alumina. 

A fully rare-earth-exchanged zeolite equilibrates at a high UCS. whereas a non-rare-earth zeolite equilibrates at a very low UCS in the range of 24.25 [3]. All intermediate levels of rare-earth-exchanged zeolite can be produced. The rare earth increases zeolite activity and... 

These metals, when deposited on the E-cat catalyst, increase coke and gas-making tendencies of the catalyst. They cause dehydrogenation reactions, which increase hydrogen production and decrease gasoline yields. Vanadium can also destroy the zeolite activity and thus lead to lower conversion. The deleterious effects of these metals also depend on the regenerator temperature the rate of deactivation of a metal-laden catalyst increases as the regenerator temperature increases. 

T5 pically, supported metal catalysts are used in order to hydrogenate or oxidize the educt to the desired compound. Such catalysts often contain a metal (for example, 0.5-5 wt.%), which was deposited on the surface of a support (e.g., Si02, AI2O3, Ti02, zeolites, activated carbon) by means of an appropriate catalyst synthesis procedure (Figure 1). 

A somewhat unusual copper catalyst, namely a zeolite in which at least 25% of its rhodium ions had been exchanged by Cu(II), was active in decomposition of ethyl diazoacetate at room temperature 372). In the absence of appropriate reaction partners, diethyl maleate and diethyl fumarate were the major products. The selectivity was a function of the zeolite activation temperature, but the maleate prevailed in all cases. Contrary to the copper salt-catalyzed carbene dimer formation 365), the maleate fumarate ratio was found to be relatively constant at various catalyst concentrations. When Cu(II) was reduced to Cu(I), an improved catalytic activity was observed. 

These results obtained at room temperature favor the specific interactions of a "ir-complex" type. Similar conclusions were drawn from 1-and trans 2-butene adsorption studies on NaY zeolites as well as on HY zeolite activated at 750 K (29). ... 

Our emphasis here is not on catalyst preparation and structure, but we need to describe briefly the preparation and properties of several major catalysts amorphous silica, y-alumina, zeolites, activated carbon, and supported metals. 

The choice of the appropriate catalyst system will have an impact on the potential formation of the heavy polymers and coke. Cracking the high molecular weight precursors catalytically will significantly reduce the possibility of thermally degrading these components. The zeolite activity should be optimized in combination with an active matrix selective to upgrading the heavy feed components. 

Usually best choice for desiccation of gases (<3% water) such as argon, helium, hydrogen, chlorine, hydrogen chloride, sulfur dioxide, ammonia, air, and chemical classes such as aliphatics, aromatics, halogenated compounds, oxygenated compounds (silica gel, zeolites, activated alumina all alternatives some regenerable, some not). 

To determine the influence of the degree of exchange on zeolite activity, studies were done on samples la, 2a, and 4a (degree of NH4+ exchange 90%). Results of spectroscopic investigations on the adsorption of iV,2V-dimethylaniline in samples la, 2a, and 4a showed that only sample 4a is as active in the dark as sample 3 after pretreatment at 350°, 450°, and 550°C. Samples la and 2a appeared to be inactive in the dark. Photoirradiation of samples la and 2a yielded almost the same results as for samples 1 and 2 except for a slight increase in intensity of the spectral bands for the former samples. 

Zeolite samples that were exhaustively treated were gray in color (materials A). Portions of each treated catalyst (0.3 gram) were calcined at 500°C in oxygen for 6 hours, giving a white product (material B). X-ray analysis showed no deterioration in crystal structure on treatment with TMS and subsequent calcination. Surface area measurements using N2 adsorption at — 196°C and the Point B method are also given in Table I. The value for HY zeolite, activated as described, prior to TMS treatment was 840 m2/gram. 

Catalytic and Electron Transfer Properties. The isomerization of cyclopropane on HY zeolites activated at temperatures less than 600° C is attributed to catalysis by Bronsted acid sites (12, 13), and the activation temperature for maximum activity was in the range 300°-400°C (13). On the other hand, rearrangement of protoadamantane to adamantane proceeds by hydride ion abstraction at Lewis acid sites (lfy. Materials B, therefore, appear to have good Bronsted activity (Figure 5) and in view... 

For many reactions, especially carbonium-ion type reactions, the zeolites and the amorphous silica-aluminas have common properties. The activation energies of the processes with both types of compounds change insignificantly, and both compounds have similar responses to poisons and promotors (1, 2). In general the zeolites are far more active than the amorphous catalysts, but ion exchange and other modifications can produce changes in zeolite activity which are more important than the differences between the activities of the amorphous and zeolitic catalysts ... 

Zeolite activity, being a quite untypical phenomenon for oxidation catalysis, gave rise to several fundamental questions. The origin of the activity caused most discussion. 

Carbon Molecular Sieve Zeolite, Activated C Activated C Activated C... 

On Day 3, the manipulations conducted on Day 2 are tested. Treatments with zeolite, activated carbon, Amberlite XAD , anion and cation exchange resins are conducted and the toxicity tests initiated. 

For the paraffinic feedstocks tested, the impact of the zeolite activity is much more pronounced, and the catalyst with the highest zeolite activity and lowest mesopore activity generates the lowest bottoms yield. 

In the supported systems the catalyst can be coated on the walls of the reactor, supported on a solid substrate or deposited around the case of the light source. Many are the supported materials used in literature, such as glass beads, and tubes [69], silica-based materials [70], hollow beads, membranes [71], optical fibers, zeolites, activated carbon, organic fibers [72], and so on. 

The problem associated with zeolites as nitration catalysts will be a reversible deactivation by coke deposition, and an irreversible deactivation by framework A1 removal (acid leaching). Optimization of zeolite activity, selectivity and life will be controlled by density of acid sites, crystalline size and hydrophobic/hydrophilic surface properties. 

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