Heterogeneous Catalysts. Группа авторов
from the pockets [21]. With the catalyst formulation and reactor design in place, a pilot test on a 4 m reactor was carried out in 1911, subsequently leading to the commissioning of a full‐scale manufacturing plant at Oppau consisting of an 8 m high reactor to produce 20 tons of ammonia per day [16], which is known now as the Haber–Bosch process.
The triumph in ammonia synthesis in Germany caught on with the industrial production of methanol (from syngas). As early as 1921, George Patas in the neighboring France patented a high‐pressure process for the synthesis of methanol using copper as well as nickel, silver, and iron catalysts [22]. BASF has again sought the help of Mittasch to search for suitable catalysts. This resulted in the discovery of zinc chromite (Cr2O3–ZnO) catalyst that was used in its industrial methanol production plant at Leuna in 1923. The catalytic reactor operated at 300 atm and 300–400 °C [23, 24]. Although iron‐containing (as well as nickel) catalysts also show methanol synthesis activity, they were later excluded from the catalysts screening due to the formation of iron carbonyl (from the reaction with carbon monoxide in the syngas) during the reaction that further decomposes to metallic iron (or iron carbide) [25]. Instead of catalyzing the methanol synthesis, these iron phases are more efficient at producing hydrocarbons (the basis for Fischer–Tropsch synthesis!), which is a more exothermic reaction. For the same reason, high‐pressure steel reactors were lined with copper, silver, or aluminum [26].
In 1947, Polish chemist Eugeniusz Błasiak patented a highly active methanol synthesis catalyst containing mixed copper, zinc, and aluminum prepared by coprecipitation [27]. Using the same catalyst, the Imperial Chemical Industries (ICI) developed a low‐pressure methanol synthesis process that only required operation at 30–120 atm with sufficient kinetics at 200–300 °C and selectivity of over 99.5%. The process along with the upstream high‐pressure steam reformer was patented in 1965 [28], followed closely by another landmark patent on the synthesis of mixed oxide of copper–zinc catalyst with promoter element from groups II–IV [29]. The catalytic process and catalyst formulation have remained largely unchanged.
Using Bosch's high‐pressure reactor, Franz Fischer and Hans Tropsch of Kaiser Wilhelm Institute for Coal Research (now known as Max Planck Institute of Coal Research) found the formation of high‐molecular‐weight hydrocarbons when using iron filings at 100 atm and 400 °C. As mentioned earlier, this was an undesirable reaction during the methanol synthesis, but Fischer understood the importance of this reaction. While continuing to work on this direction, they routinely assessed a range of metal oxides, hydroxides, and carbonates and in 1926 reported that reduced iron and cobalt catalysts yielded gasoline fuels from coal‐derived syngas [30, 31]. The reaction is known as the Fischer–Tropsch synthesis (FTS), which in 1935 marked the first FTS plant commissioned by Ruhrchemie using the cobalt catalyst. By 1938, there were nine such facilities within Germany with a manufacturing capacity of 600 000 tons/annum. The cobalt catalyst (100 Co/100 SiO2/18 ThO2) used by Ruhrchemie was developed by Fischer with Meyer and later with Koch by rapidly coprecipitating hot solutions of cobalt and thorium nitrate on SiO2 (Kieselguhr diatomaceous earth) suspended in an ammonia‐containing solution [32, 33]. The irreducible thorium oxide restricts the crystallization of the cobalt metal to maintain a high dispersion. The slightly radioactive thoria has been replaced by zirconia, titania, or manganese oxide in the present‐day catalysts.
While cobalt is known to produce a large fraction of diesel and paraffin wax, the iron catalyst results in higher content of short‐chain olefins when carried out at high reaction temperatures (∼340 °C) or paraffin wax at much lower temperatures. As the reaction proceeds, the iron metal is gradually converted into iron carbide, which is an even more active phase [24, 34]. Compared with crude oil–derived fuels, the FTS‐derived diesel and gasolines are characterized by their exceptionally high cetane and octane ratings due to the high yields of straight‐chain paraffins for cobalt‐derived diesel and olefins/isomers in the iron‐derived gasoline, respectively. Although nickel and ruthenium catalysts are also active in FTS, they are rarely used as stand‐alone catalysts. Nickel, which forms carbonyl and decomposes to the metallic phase (like iron), has a high tendency to form methane instead of liquid fuels. Ruthenium, which is the most active FTS catalyst, is far more expensive than cobalt and iron to justify its bulk usage except as a promoter to cobalt catalysts. Incipient wetness impregnation is by far the most common technique for the synthesis of FTS catalysts [35].
1.3 Catalytic Cracking and Porous Catalysts
One of the earliest applications of heterogeneous catalysts in the modern petrochemical industries (crude oil refineries) can perhaps be traced to the catalytic cracking process. In the early 1920s, French engineer Eugene Jules Houdry, E. A. Prudhomme (the pharmacist who discovered the reaction) and their team developed the catalytic lignite‐to‐gasoline process, whereby lignite was first pyrolyzed to high‐boiling‐point liquid hydrocarbons, followed by vaporization and catalytic conversion to the gasoline fractions [36]. The latter step is similar to noncatalytic, high‐temperature, and high‐pressure cracking of the heavier fractions of the crude oil to produce (low octane rating) gasoline developed by Standard Oil Company in the United States a few years earlier. Efforts were made to boost the octane rating of the synthetic gasoline including trial using aluminum chloride as the cracking catalyst but was found to be economically unfeasible. Thomas Midgley and Charles Kettering of General Motors patented the addition of tetraethyl lead to gasoline to improve its octane rating substantially, which was rather successful commercially but was banned worldwide many years later due to the release of toxic exhaust fumes [37]. Houdry discovered a more environmentally benign solution, that is, use of Fuller's earth, a naturally occurring aluminosilicate layered clay, as a cracking catalyst to produce extremely high‐quality gasoline from heavy crude.
Despite not having found much success in France, where the process was deemed not commercially viable, Houdry brought his catalytic cracking process to the United States in the 1930s for further development with Sonoco Vacuum Oil Company (later Mobil Oil Corporation and now ExxonMobil) and adapting the technology to the petrochemical processing. Upon overcoming various reactor engineering challenges to cope with the rapid catalyst coking during the cracking reaction, the Houdry process became a phenomenal success that revolutionized the petrochemical industry. His inventions paved the way for the development of the modern fluidized catalytic cracking (FCC) process, where catalysts were fluidized for continuous looping between the catalytic cracking reactor and adjacent regenerator unit (to remove coke by air oxidation). The Houdry process was so successful that the production of synthetic silica–alumina and magnesia–silica catalysts was commenced in the 1940s to meet the needs for catalytic cracking reaction [38]. In fact, the silica–alumina catalyst is still used to this day in industrial FCC, but in the form of synthetic zeolites, which have a much higher surface area than the clay minerals.
Synthetic zeolites, which constitute crystalline microporous (0.3–2.0 nm pores) aluminosilicates, have been actively developed since the late 1950s by the Union Carbide and Mobil Oil Corporation, resulting in the discovery of zeolites A (Linde Type A) and X (Linde Type X) in 1959 [39], zeolite Y (Linde Type Y) in 1964 [40], and ZSM‐5 in 1972 [41, 42]. These landmark catalysts continue to find important applications not only in FCC but also in the isomerization of hydrocarbons, synthesis of specialty chemicals, methanol‐to‐hydrocarbon conversions, and catalytic deNOx, with a great deal of advancement achieved in the last decade in the conversion of biomass, among many others. Excellent accounts on the fundamentals as well as the state‐of‐the‐art progress in some of these topics are highlighted in Chapter 33 (on the conversion of lignocellulose to biofuels), Chapter 34 (on the conversion of carbohydrates to high‐value products), and Chapter 38 (on the abatement of NOx). In fact, the discovery of new zeolites has been thriving since the 1980s, with a unique set of material compositions, frameworks, and pore dimensions being discovered annually. A large database of zeolites is maintained by the International Zeolite Association since 1977 through the Atlas of Zeolite Structure Types [43]. While silicate and aluminosilicate zeolites dominate a large