Propene is a key building block for the petrochemical industry whose demand is increasing strongly in recent years, even faster than that of ethene. The availability of propene is limited, and therefore, efforts to optimize its production are being pursued. On the occasion of the 75th anniversary of the first FCC unit, we analyze some recent advances that have been achieved in the understanding and development of zeolites aiming to increase the production of light olefins as petrochemical building blocks by means of catalytic cracking. We discuss a selected group of emerging strategies in zeolite engineering that have great prospects for research and that we consider could impact the sector in the near future. These include advances in crystal engineering and hierarchization achieved through bottom-up and top-down approaches, composite materials, tuning of the location of active sites among the different crystallographic positions available, and, importantly, how to characterize these modifications and their impact on the catalysis. Finally, we survey what advances are actually being implanted into the current industrial practice and conclude with a reflection on the future of zeolite research to satisfy light olefin demand.

The Cu­(I)-catalyzed reaction of the platinum butadiynyl complex trans-(C6F5)­(p-tol3P)2Pt­(CC)2H and rhenium cyclopentadienylazide complex (η5-C5H4N3)­Re­(CO)3 yields the 1,2,3-triazole trans-(C6F5)­(p-tol3P)2PtCCCCHN­((η5-C5H4)­Re­(CO)3)­NN (54%), which upon treatment with Re­(CO)5OTf or Re­(CO)5Br affords Re­(CO)5 +TfO– or cis-Re­(CO)4Br adducts derived from attack at N(3) (84–98%). The crystal structures of solvates of these three complexes are compared, but attempts to metalate the CH groups were unsuccessful. However, the reaction of monometallic trans-(C6F5)­(p-tol3P)2PtCCCCHN­(CH2C6H5)­NN and MeI gives an N(3)-methyl triazolium salt (81%), which upon addition of Ag2O and [RhCl­(cod)]2 yields the N-heterocyclic carbene complex trans-(C6F5)­(p-tol3P)2PtCCC ... C­(RhCl­(cod)) ... N­(CH2C6H5) ... N ... N­(Me). Further experiments and analyses suggest that CH derivatization is possible only when the 1H NMR chemical shift is downfield of ca. δ 7.9 ppm. Electropositive metal fragments generally effect upfield shifts, meaning that insulating spacers, electronegative ligands, and/or new chemical methodologies will be required to construct tetrametallic arrays via click chemistry.

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Looking back at the history of industrial chemistry, it can undoubtedly be declared that the impact of the introduction of zeolites into refi nery operations has been revolutionary as it resulted in a signifi cant increase in gasoline yield from catalytic cracking, leading to more ef fi cient utilization of the petroleum feedstocks. Based on this successful entry into the industrial scene, zeolites quickly found many applications in petroleum processing in subsequent years; however, catalytic cracking still by far is the largest volume of zeolite catalyst consumer worldwide. Today, fl uid catalytic cracking (FCC) catalysts account for more than 95 % of the global zeolite catalyst consumption (primarily USY zeolite). Fluid catalytic cracking units (FCCUs) around the world currently process around 15 million barrels per day and constitute the main conversion process in a typical fuels refi nery. Primary output from FCC units is gasoline, and due to their pivotal role in fl uid catalytic cracking, it can be stated that zeolite catalysts have been fueling our industrialized society by providing majority of the transportation fuels used, thus having direct impact on the global economy. Furthermore, in order to enhance the light olefi n yields from FCCUs as a result of the increasing demand for building blocks for the chemical industry such as propylene and butylene, the FCC catalyst compositions are being modifi ed by tuning their formulations and introducing different types of zeolite structures as additives. Using these zeolite-based catalyst formulations, many new FCC units worldwide also provide the critical starting points for (petro)chemical value chains. Hence, for the global supply of both fuels and chemicals, zeolitebased FCC catalysts are of paramount strategic and commercial importance. History of Fluid Catalytic Cracking (FCC)Since the 1800s, thermal cracking had been in practice to break down crude oil into functional components. The fi rst commercial use can be traced back to the days of Samuel M. Kier, a salt well entrepreneur, who started refi ning crude into lamp oil that can burn with lesser smoke and odor [ 1 ]. By 1854, he and his partner, John T. Kirkpatrick, pioneered the fi rst oil refi nery in Pittsburgh, Pennsylvania. Following their success, the market became saturated with refi ners and by the end of 1860s, 58 refi neries were in operation in Pittsburgh alone.In the early 1900s, engineering advancement in combustion engines gave rise to a demand for gasoline fuel. Several patents of thermal cracking techniques emerged with the fi rst commercial success in such a process by Dr. William M. Burton of Standard Oil Company of Indiana [ 2 ]. In the "Burton cracking process" (US Patent 1049667), gasoline production can be signifi cantly increased by heating crude oil in excess of 750 °F (ca. 400 °C) in a still under pressure of around 90 psig [ 3 ]. This was the primary method of gasoline production before catalytic cracking was introduced to the refi ning industry in the 1940s.Almer M. M...

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