Alumina matrix

Eig. 2. SEM photomicrograph of poHshed section of neat eutectic alumina-2inconia abrasive grain showiag white 2inconia ia dark alumina matrix. 

Catalyst composition and feed chloride have a noticeable impact on hydrogen yield. Catalysts with an active alumina matrix tend to increase the dehydrogenation reactions. Chlorides in the feed reactivate aged nickel, resulting in high hydrogen yield. 

Similar experiments with copper dispersed on AI2O3 did not show any unusual behavior of the Al(ls) or Cu(2p) photolines. In this case, the copper could be easily cycled between CuO under oxidative conditions, to Cu metal during reducing conditions. We observed only a slight shift (<0.4 eV) of the aluminum (Is) line upon initial heating, which was attributed to the loss of water in the alumina matrix. 

An alumina matrix may be prepared with high pore density (more than 60 %) and pore diameters ranging from 5 to 250 nm. Ruiz-Hitzky et al. [214] immobilized GOD in nanoporous alumina membranes with regular hexagonal arrays of highly ordered cylindrical pores aligned perpendicularly to the membrane surface. GOD was anchored in the membrane by the highly hydrophilic chitosan biopolymer. Full activity was maintained for at least 50 hours. 

The earliest catalyst was made from clay later, synthetic beads from siUca-alumina were introduced. In the early 1960s, catalysts were introduced that employed up to 10% X or Y zeolite in a silica-alumina matrix. 

Source of Silica. Silica can migrate either from free silica present in the cracking catalyst or from the silica alumina matrix but not as readily from the zeolite. Figure 11 shows SEM-EDAX silicon scans of cerium/alumina steamed in the presence of these three sources of silica. Again, the bright dots represent silicon. Qualitatively the sample steamed with pure silica contains more silicon than the sample steamed with silica-alumina. The sample steamed with zeolite shows silicon at the surface of the cross-sectioned particle but little in the interior. The surface silicon comes from dusting of the particle with very finely divided zeolite. 

How to Solve the Deactivation Problem. Solutions to the deactivation problem are difficult. The patent literature (42) has claims that either sodium, manganese or phosphorous added to alumina prevents deactivation by silica. In addition, removal of matrix silica from cracking catalyst formulations should prevent further deactivation because zeolitic silica, as we have shown, migrates more slowly. There is at least one patent relating to very high alumina matrix cracking catalysts (43). Another solution is to use more active SOx catalysts such as magnesia-based materials. 

For the cracking of fraction No.6, a higher c/o-ratio was required for H2 compared with H6 in order to obtain a given conversion level. This reflects the additional activity supplied by the alumina part of the matrix. The contribution of the alumina in the matrix is also seen when fraction No. 6 is cracked over spray dried samples of the matrices only. At a c/o-ratio of 3.0, conversions of 33% and were obtained using the kaolin and the kaolin-alumina matrix, respectively. The tendency for higher coke and gas production at the expense of gasoline over catalyst H6 compared with H2 is also seen for oil No. 6. 

In China, most of the traditional RFCC catalysts (such as Orbit, DVR, and MFC mentioned above) are based on alnmina matrix, and the most widely used materials for alumina matrix preparation are alumina sol and modified active alumina [4]. Alumina matrix combines the virtnes of alumina-sol (better attrition resistance and coke selectivity) and active alnmina (higher cracking activity), thus improving the cracking activity and selectivity of the catalysts. However, the coke selectivity of the alumina matrix is nnsatisfactory when processing resid feed due to the insufficient amount of meso/macropores and higher concentration of acid sites. 

To improve bottoms cracking activity and coke selectivity of RFCC catalysts, novel zeolites and matrices have been developed recently. Commercial results showed that both VRCC-1 catalyst containing SOY zeolite and RSC-2006 based on silica modified alumina matrix have demonstrated excellent bottoms cracking capability and... 

Colloidal palladium particles in an alumina matrix catalize the hydrogenation of ethene to ethane. The following data describe various catalyst preparations ... 

The heterogeneous catalysts employed in cracking are acidic materials composed of 3 to 25% (wt) of zeolites embedded in a silica-alumina matrix. Zeolites are crystalline aluminosilicates possessing a network of uniform pores whose walls hold the catalytically active acid sites. The reactant molecules pass through the pores and react within the zeolites. 

Paraffin isomerisation Pt on H-mordenite zeolite in alumina matrix... 

Figure 12. (A) SIMS spectrum of a nickel complex showing characteristic ions (Cp = C5H5). (B) SIMS spectrum of the same complex in an alumina matrix.

Indentation crack paths in alumina matrix composites containing 20 vol% of particles of (a) TiN and (b) Cr3C2. The alumina matrix is the darker phase in each case. 

Walker, C.N., Borsa, C.E., Todd, R.I., Davidge, R.W. and Brook, RJ. Fabrication, characterisation and properties of alumina matrix nanocomposites , British Ceramic Proc. 53 (1994) 249-264. 

In this chapter, we describe the synthesis and characterisation of the microstructure and properties of layered-graded alumina-matrix composites through liquid infiltration. This approach is relatively simple and offers excellent control over the depth of the graded layer. The presence of a graded dispersion of reinforced particles in the alumina matrix has a profound influence on the physical and mechanical properties of the composites. An overview of the infiltration kinetics and the use of the infiltration process as a new philosophy for tailoring novel graded ceramic systems are also presented. 

Liquid infiltration processing of layered-graded alumina-matrix composites. 

Mishra, R.S., Mukheijee, A.K., Processing of high hardness-high toughness alumina matrix nanocomposites, Mater. Sci. Eng. A, 2001, 301 97. 

The possibility to obtain a uniformly dispersed composite powder was shown for the a-Fe-Al203 system where metal particles with an average size of 55 nm were formed in an amorphous/nano alumina matrix.18 Other studies attempting to obtain dense bulk composites based on the sol-gel route using conventional pressure-assisted sintering ( 1400°C and an applied force of 10 MPa) resulted in a coarse microstructure.16 However, if reaching theoretical density is not a necessary requirement, a porous ceramic microstructure containing nanometer-sized metal particles can be used as a catalytic material.19 Certain combinations of composite materials demand... 

Oh, S.T., Sando, M., Sekino, T. and Niihara, K., Processing and properties of copper dispersed alumina matrix nanocomposites , NanostructuredMater, 1998 10 267-272. 

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