It is beyond the scope of this chapter to describe commercial FCC catalysts in depth. These types of catalysts are extensively detailed in the following chapter and the reader is referred to the data provided there. In this section we will mainly discuss the application of FCC catalysts that can be used directly in the pyrolysis process rather than upgrading of pyrolysis oils. Whilst many catalysts have shown promise, it has proved important to use robust commercially available catalysts in the development of catalytic pyrolysis as a commercially viable technology. The FCC process allows for efficient conversion of high-boiling point and high — molecular weight hydrocarbon fractions of crude oil into more valuable petrol fuel grades.206 Their use has been refined since their introduction in the 1960s (for petroleum refining) to allow for high performance, long-life and re-activation in fluidised bed systems. Scherzer has given an excellent view on the design of these catalysts as applied to zeolite-Y.207 How these catalysts deactivate through a combination of coking, poisoning and attrition and the deactivation of these catalysts is an area of great interest both industrially and academically.208 The synthesis of zeolite materials usually provides small particles that can not be readily sintered into larger materials because of their highly crystalline nature and these particles are too fine for commercial applications. The basic design of these commercial catalysts allows development of catalyst particles that can be readily supported in a fluidised bed, and an FCC catalyst usually consists of a mixture of activated alumina (as described earlier), the active zeolite, a binder (normally a silicate) and an inert matrix (a clay or related material; kaolin is often used). The alumina and the binder provide both mechanical and thermal robustness. The inert matrix allows the formation of larger particles (a few micron in diameter) and pellets (less than 100 micron diameter). Careful synthetic processing is required to allow the hydrocarbons access to and from the active phases within these complex systems. Coking is the major problem (deactivating the active sites as well as physically blocking pore systems) and in use the catalysts are continually re-circulated between the reactor (the riser) and the oxidising regeneration chamber.

FCC catalysts have been widely used for catalytic pyrolysis of polymers,209 biomass133 as well as various vegetable/plant oils.210 Samolada et al. found that FCC catalysts were effective in the pyrolysis of a bio-oil producing low coke and gas yields compared to several other zeolite and transition metal catalysts.133 The catalyst also effected the greatest degree of de-hydrolysis but the stability of the oil was somewhat lower than other catalysts.133 Ioannidou et al. found that FCC catalysts were effective in the pyrolysis of corn cobs and stalks providing a higher quality bio­oil than in the absence of catalyst.27 A similar finding was made by Antonakou and co-workers who found that the use of an FCC catalyst greatly improved the stability of the pyrolysis oil compared to thermal pyrolysis in its absence.142 Work by Lu et al. reports that FCC catalysts (for pyrolysis of biomass) based on a combination of HZSM-5 and y-Al2O3 are more effective in improving both isomerisation and aromatisation than a zeolite-Y based material.211 Zhang et al. have recently published excellent work on FCC catalysed pyrolysis of corn cobs.212 They compared different relative volumes of catalyst and biomass in a fluidised bed and found the ratio had a profound effect on the product distribution. Whilst fresh catalyst resulted in greater dehydration of the corn, used catalyst resulted in greater oil yields. It was also found that the improvement in stability of the product oil was related to the reduction of some active oxygenated hydrocarbon species that promoted polymerisation.212 The use of FCC catalysts to upgrade bio-oil produced by pyrolysis of lignin through the removal of polymerisation active phenols has recently been reported by Gayubo et al.213 These results all point to the effectiveness of these catalysts. It should be stressed that the majority of pilot-scale testing of these technologies for biomass pyrolysis has been largely dominated by these catalysts.

FCC type catalysts appear successful for pyrolysis of heavy oils but the amount used has to be carefully controlled in order to optimise the yield of oil and an ideal product distribution.147 In polyolefin pyrolysis FCC catalysts have been shown to be particularly effective with good production of lighter hydrocarbons and good aromatic content. Indeed, the performance of FCC catalysts appears to be significantly better than zeolite-Y or ZMS-5 with not only improved liquid yields but a greater proportion in the gasoline/petrol composition range.214 The reason for the more effective behaviour of these catalysts appears to be the bimodal pore size distribution arising from the combination of microporous and mesoporous structures exhibited by the different materials used in the formulation of these materials.215 One of the more consistent findings for these catalysts for polymer pyrolysis is that spent (i. e. after cycling through the reactor and regenerator in typical FBRs) materials have better than expected or even better performance characteristics than fresh catalysts and this appears to be true for a range of polymers and process conditions.216,217