Mittasch catalyst

The actual problem in studpng the surface chemistry of the "real" catalyst becomes evident from the inspection of an electron micrograph from the Mittasch catalyst reproduced in Fig. 6.1 [7]. The "doubly promoted" catalyst is formed from a precursor consisting essentially of Fe304 with small concentrations of potassium, aluminum, and calcium oxides as listed in the first row of the table of Fig. 6.1. The surface composition differs considerably from that of the bulk and changes further upon reduction. The working catalyst consists of particles with about 30 nm size and a specific surface area of around 20 m /g. Under reaction conditions, these... 

In the original work on catalytic ammonia synthesis, Haber [41] had used an osmium catalyst, but this metal was much too expensive to be the basis of the large-scale industrial plants. In the long search for alternatives to the Mittasch catalyst, alkali-promoted ruthenium was found to exhibit specific activity, which is even superior to the iron catalyst [42] and which was subsequently developed to an industrial catalyst [43]. The Mittasch catalyst is cheap and the alumina promoter provides a high specific surface area. This situation is different with Ru catalysts that are prepared as small particles on a suitable support. Figure 1.1 was a t)q)ical electron microscopic picture from such a catalyst particle on MgAl204 (spinel) support [44]. 

Bosch and co-workers devised laboratory reactors to operate at high pressure and temperature in a recycle mode. These test reactors had the essential characteristics of potential industrial reactors and were used by Mittasch and co-workers to screen some 20,000 samples as candidate catalysts. The results led to the identification of an iron-containing mineral that is similar to today s industrial catalysts. The researchers recognized the need for porous catalytic materials and materials with more than one component, today identified as the support, the catalyticaHy active component, and the promoter. Today s technology for catalyst testing has become more efficient because much of the test equipment is automated, and the analysis of products and catalysts is much faster and more accurate. 

The catalyst was reformulated by Alwin Mittasch, who synthesized some 2500 different catalysts and performed more than 6500 tests. They arrived at a triply promoted catalyst consisting of a fused iron catalyst, with AI2O3 and CaO as structural promoters and potassium as an electronic promoter. The process was first commercialized by BASF, with the first plant located in Oppau in Germany producing 30 tons per day in 1913. The plant initially produced ammonium sulfate fertilizer, but when the First World War broke out it was redesigned to produce nitrates for ammunition. The plant was expanded and in 1915 it produced the equivalent of 230 tons ammonium per day. 

Louis Schmerling and V. N. Ipatieff Early Studies of Multicomponent Catalysts Alwin Mittasch... 

To conclude, it is worth recording the advice given to the author at the very start of his career by the veteran catalytic chemist Alwin Mittasch, who had been Fritz Haber s officer in charge of catalyst research for the ammonia synthesis In all catalytic studies only the very purest is good enough . 

Early Studies of Multicomponent Catalysts Alwin Mittasch... 

The promoted iron catalyst to accelerate this reaction was discovered by Bosch, Mittasch, and coworkers, in 1909. Consequently, the industrial process for the production of ammonia is named the Haber-Bosch process. In this process, ammonia is formed by the reaction between N2 and H2 using a Fe304 (magnetite) catalyst promoted with A1203, CaO, K20, and other oxides. 

NH, NHj, NH3, and H species are together larger than the free-site fraction so that Langmuir-Hinshelwood conditions, with only one significant chemisorbed intermediate, do not obtain. In fact, quite early work had already indicated 54) that, in technical catalysis for NH3 synthesis, it is the bonding of Nj (as N) to the catalyst surface which determines the overall rate of the reaction. Correspondingly (55), at moderate temperatures at W, NH3 decomposes giving imide and nitride species on the surface. The rate of decomposition of the nitride species (chemisorbed N) as an intermediate in the NH3 synthesis reaction at Fe was shown by Mittasch et al. (5(5) to be equal to that of NH3 production. 

Alwin Mittasch contributed decisively to this revolutionary development by embarking on a tireless search for a technically useful ammonia catalyst and by unearthing, during this search, valuable knowledge from which we benefit to the present day. 

It was characteristic of Mittasch s keen perception that during his efforts to find a technical synthesis catalyst, he remained conscious of the... 

It was not in Mittasch s character to be satisfied with this conspicuous achievement. Parallel to extensive studies on the influence of pressure, temperature, gas composition, catalyst poisons and other factors on the synthesis reaction, he worked toward new types of multi-component catalysts for a great number of other catalytic gas reactions. With his associates Ch. Beck, C. Muller, and Ch. Schneider, he thus discovered efficient catalysts for the water gas reaction, for hydrogenations in the gas phase (among which the synthesis of alcohols and hydrocarbons from carbon monoxide and hydrogen is particularly noteworthy), for the production of nitric acid via the oxidation of ammonia, and for many more industrial processes which are the backbone of large segments of our present chemical industry. 

In the "Ammoniak laboratory at Oppau, a multitude of projects, including many of a non-catalytic nature, were investigated under Mittasch s administration. Yet, the study of catalysis remained closest to his heart. To an increasing extent he initiated theoretical studies to shed some light on the chemical and physical factors that make a multi-component solid catalyze a specific reaction. Primarily, these scientific investigations centered around those catalysts that had previously been found by empirical methods at the Ammoniak laboratory. 

Ammonia has been produced commercially from its component elements since 1909, when Fritz Haber first demonstrated the viability of this process. Bosch, Mittasch and co-workers discovered an excellent promoted Fe catalyst in 1909 that was composed of iron with aluminium oxide, calcium oxide and potassium oxide as promoters. Surprisingly, modem ammonia synthesis catalysts are nearly identical to that first promoted iron catalyst. The reaction is somewhat exothermic and is favoured at high pressures and low temperatures, although, to keep reaction rates high, moderate temperatures are generally used. Typical industrial reaction conditions for ammonia synthesis are 650-750 K and 150-300 atm. Given the technological importance of the... 

---