Catalysts matrix

An active matrix provides the primary cracking sites. The acid sites located in the catalyst matrix are not as selective as the zeolite sites, but are able to crack larger molecules that are hindered from entering the small zeolite pores. The active matrix precracks heavy feed molecules for further cracking at the internal zeolite sites. The result is a synergistic interaction between matrix and zeolite, in which the activity attained by their combined effects can be greater than the sum of their individual effects [2J. 

Matrix Activity. Increasing the catalyst matrix activity increases the octane. 

Engelhard Corporation, Catalyst Matrix Properties Can Improve FCC Octane, The Catalyst Report, TI-770. 

The selectivity and activity of the catalyst matrix will continue to improve. The emphasis on bottoms cracking and steady reduction in the reaction residence time demands an increase in the quantity of active matrix. 

Matrix is a substrate in which the zeolite is imbedded in the cracking catalyst. Matrix is often used as a term for the active, non-zeolitic component of the FCC catalyst. 

In a bulk silica matrix that differs from the silica nanomatrix regarding only the matrix size but has a similar network structure of silica, several kinetic parameters have been studied and the results demonstrated a diffusion controlled mechanism for penetration of other species into the silica matrix [89-93]. When the silica is used as a catalyst matrix in the liquid phase, slow diffusion of reactants to the catalytic sites within the silica rendered the reaction diffusion controlled [90]. It was also reported that the reduction rate of encapsulated ferricytochrome by sodium dithionite decreased in a bulk silica matrix by an order of magnitude compared to its original reaction rate in a homogeneous solution [89], In gas-phase reactions in the silica matrix, diffusion limitations were observed occasionally [93],... 

On non-zeolitic particles in the absence of a vanadium passivator, vanadium (when present at the 0.4 wt% level) makes a greater contribution to contaminant coke and hydrogen yields than nickel at constant surface area and metals loading. Incorporation of a vanadium passivator into the catalyst matrix can greatly alter the selectivity effects of vanadium, and can essentially negate its effect on non-zeolitic particles as in the case of magnesium. 

Silica-magnesia matrices have not yet been properly evaluated as an RCC catalyst matrix. However, such a matrix in conjunction with stabilized zeolite might provide an attractive matrix with a Kaolin-enhanced dual pore structure. Silica-magnesia matrices are notorious for their poor regeneration characteristics. When prepared by the dual pore Kaolin-enhanced method, they might be easier to regenerate and, thereby, open up a new family of residuum catalysts. Such catalysts have not yet been explored. 

The estimates in Table IX represent the minimum effect of the loss of micropore volume. Pore-mouth constrictions which lead to partial or complete micropore plugging would serve to increase the contribution of loss of micropore volume to density change. No such pore plugging is expected to occur in the (mesoporous) catalyst matrix or in the mesoporous material that is generated during crystalline zeolite destruction. 

However, the thermal conductivity of the catalyst matrix is usually larger than that of the gas. This means that the external gas-catalyst heat transport resistance exceeds the thermal conduction resistance in the catalyst particles. The temperature and concentration profiles established in a spherical catalyst are illustrated for a partial oxidation reaction in Figure 4. 

In some cases, researchers have recorded the reference spectra at the same temperature and in the same gas atmosphere as were applied for the respective measurements of the sample. Particularly in the NIR range, a temperature correction can become necessary. For example, Sels et al. (2001) used a spectrum of the catalyst matrix (layered double hydroxide) suspended in methanol and aqueous H2O2. Brik et al. (2001) recorded their BaSC>4 reference spectra at various temperatures. Lu et al. (2005) recorded the spectra of their catalyst support, CaC03, as references under the conditions of the catalytic reaction, that is, in a mixture of ethene or propene in O2 and He at 473 K. Rao et al. (2004) heated their reference material to reaction temperature to generate the baseline. 

The micro properties cannot be determined easily. Moreover, due to the complexity of diffusion of reactants in a solid catalyst matrix, models taking the micro properties into account tend to be very complex and inaccurate [1], Therefore, the micro properties are usually accounted for by a lumped parameter, the so-called effective diffusion coefficient De. For solid catalyst particles this approach has proved to be very useful, provided that the particles can be regarded as homogeneous on a micro scale. However, if this is not the case, such as for zeolite in an amorphous matrix, care should be taken in using this approach [2,3]. 

For very low values of the effectiveness factor the penetration depth of a reactant in the solid catalyst matrix is very small. Since the curvature of the surface element can be neglected, the Laplace operator reduces to... 

Figure 1 shows the matrix surface area of conunercially aged Ecat for four types of cracking catalyst. Each set of data represents one type of cracking catalyst deactivated in different conunercial FCC units. The four types of catalysts were chosen fOT their wide range of matrix surface areas. Although the fresh catalyst matrix surface area for each catalyst type is similar, the equilibrium matrix surface area decreases by as much as fifty percent with increasing Na The variation of matrix surface could be attributed to other... 

The rate of vanadium mobility in FCCU s is dependent on many operating factors. These might be whether the unit is operated in lull or partial combustion, which will effect the average oxidation state of the vanadium. Other factors will be freshness of the vanadium, presumably older vanadium has had more of an opportunity to react with the catalyst matrix and become immobile. Steam concentration in the regenerator, catalyst make-up rate, temperature, and two-stage regeneration will all effect the mobility of vanadium. 

Pore size. The pore size distribution of the catalyst matrix plays a key role in the catalytic performance of the catalyst. An optimum pore size distribution usually helps in a balanced distribution of smaller and larger pores, and depends on feedstock type and cracking conditions. The pore size distribution of the matrix changes when another component is added e.g. by adding 35-40% kaolin to a silica-alumina gel, a pore structure with a significant amount of micropores can be obtained. Figure 27.9 Pore volume. Pore volume is an indication of the quantity of voids in the catalyst particles and can be a clue in detecting the type of catalyst deactivation that takes place in a commercial unit. Hydrothermal deactivation has very little effect on pore volume, whereas thermal deactivation decreases pore volume. 

Material Balance of Gaseous NO and NHj in the Porous Catalyst Matrix... 

The results shown in Fig. 2 suggest that the fast deposition of additive coke occurred mainly in the top zone as ARO passed through the catalyst bed, resulting in a much higher amount of coke on catalyst than other zones. Since the additive coke has much less influence on catalyst aaivity than catalytic coke, we conclude that the major pan of additive coke formed from large molecular weight R+AT deposited on the catalyst matrix, not affecting the active acid sites of the zeolite as much as catalytic coke. 

Stability of an FCC Catalyst Matrix for Processing Gas Oil with Resid... 

While samples 24CD and CPS have similar or lower MAT activities compared to ECAT samples the zeolite surface areas of the former are higher. Therefore it can be concluded that modifications in samples 24CD, 48CD and CPS involves catalyst matrix properties rather than zeolite properties. This is consistent with the observations of Pompe et al. [2]. 

The pore size distribution of the catalyst matrix is important for the catalytic performance. The optimal matrix pore size distribution will depend on a balance of mesopores and macropores depending on feedstock quality and reactor conditions (e.g. conventional vs. short contact time riser operation). SAM-technology catalysts (SPECTRA, RESIDCAT, ULTIMA) exhibit different pore size distributions that are matched to various types of feedstock and unit conditions. Figure 5 exhibits typical pore size distribution of SPECTRA-944, SPECTRA-444 and ULTIMA-444 catalysts. Since the only differentiating characteristic of these three catalysts is the matrix formulation, the pore size distribution variation is characteristic of the different matrix design ... 

All industrially-produced methanol is made by the catalytic conversion of synthesis gas containing carbon monoxide, carbon dioxide, and hydrogen as the main components. Methanol productivity can be enhanced by synthesis gas enrichment with additional carbon dioxide to a certain limit [14]. However, a C02—rich environment increases catalyst deactivation and shortens its lifetime, and produces water which adversely affects the catalyst matrix stability resulting in crystallite growth via hydrothermal synthesis phenomena [14]. Thus, a special catalyst has been designed to operate under high C02 conditions. This catalyst s crystallites are located on energetically stable sites that... 

The catalytic behavior of enzymes in immobilized form may dramatically differ from that of soluble homogeneous enzymes. In particular, mass transport effects (the transport of a substrate to the catalyst and diffusion of reaction products away from the catalyst matrix) may result in the reduction of the overall activity. Mass transport effects are usually divided into two categories - external and internal. External effects stem from the fact that substrates must be transported from the bulk solution to the surface of an immobilized enzyme. Internal diffusional limitations occur when a substrate penetrates inside the immobilized enzyme particle, such as porous carriers, polymeric microspheres, membranes, etc. The classical treatment of mass transfer in heterogeneous catalysis has been successfully applied to immobilized enzymes I27l There are several simple experimental criteria or tests that allow one to determine whether a reaction is limited by external diffusion. For example, if a reaction is completely limited by external diffusion, the rate of the process should not depend on pH or enzyme concentration. At the same time the rate of reaction will depend on the stirring in the batch reactor or on the flow rate of a substrate in the column reactor. 

A key issue in the activity of these catalysts concerns the specific role of the Cu and Cr active sites which are expected to be located on the surface of the catalyst particles. Since both Cu(II) and Cr(III) are paramagnetic, EPR spectroscopy can be used to identify the nature of the heterometallic species within the catalyst matrix after different thermal and chemical treatments. However, a detailed picture of the local environment of tlie transition metal center camiot be obtained by conventional continuous wave EPR spectroscopy alone. These can, nevertlieless, be obtained by pulsed EPR methods, namely the electron spin echo envelope modulation (ESEEM) tecluiique. 

To this point we have dealt only with transport effects within the porous catalyst matrix (intraphase), and the mathematics have been worked out for boundary conditions that specify concentration and temperature at the catalyst surface. In actual fact, external boundaries often exist that offer resistance to heat and mass transport, as shown in Figure 7.1, and the surface conditions of temperature and concentration may differ substantially from those measured in the bulk fluid. Indeed, if internal gradients of temperature exist, interphase gradients in the boundary layer must also exist because of the relative values of the pertinent thermal conductivities [J.J. Carberry, Ind. Eng. Chem., 55(10), 40 (1966)]. 

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