Ammonia catalysts, basic study

Basic Study of Ammonia Catalysts and Water Gas Shift Catalysts... 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

For metals promoting other metals, an interesting case was studied by Hurst and Rideal.2 In the combustion of mixtures of hydrogen and carbon monoxide, using copper as the basic catalyst the ratio of the gases burnt depends on the temperature, and also on the amount of small additions of palladium made to the copper. The proportion of carbon monoxide burnt is increased by addition of palladium, a maximum proportion of carbon monoxide being burnt when 0-2 per cent, of palladium is. present. With further amounts of palladium, the ratio CO H2 burnt falls off slowly until, with 5 per cent, palladium, it is nearly the same as with pure copper. This effect of palladium is ascribed to the introduction of a new type of surface, the line of contact between palladium and copper, though the proof that this is the cause of promotion is perhaps not complete. Mit-tasch and others,3 in elaborate studies of the promotion of various metal catalysts, particularly molybdenum, for the synthesis or decomposition of ammonia, concluded that the formation of intermetallic compounds... 

The electroreduction of the complexes [Fe Cp( / -arene)][PF6] was first studied in basic aqueous medium and ethanol. It was found that the complexes [Fe ( 7 -C5H4R)( 7 -C6Me6)] (R = H or C02 ) are both initiators for ETC catalyzed selfdecomposition and redox catalysts for the reduction of water to dihydrogen on mercury cathode [352]. The reduction of water is a side reaction of the ETC catalytic process and limits its coulombic efficiency (Scheme 41). On such a cathode, the surtension of the reduction of water is very high, which makes this electrode especially suitable for the study of metal ions in such a medium. During this study, it was found that the most stable Fe complex [Fe ( / -C5H5)( -C6Me6)], also catalyzes the cathodic reduction of nitrates to ammonia in the same basic aqueous medium (pH 13) [353, 354]. 

The adsorption of ammonia, pyridine, trimethylamine, and triethylamine on silica and silica-alumina was studied microcalorimetrically by Cardona-Martinez and Dumesic (18, 105). The calorimetric results of this study were correlated successfully in terms of Drago parameters for each catalyst. These parameters describe well the acidic properties of silica and the strongest sites (Lewis acid sites) on silica-alumina and may allow the prediction of heats of adsorption for a wide range of basic molecules with known Drago parameters on these sites. Parameters to describe the strength of the Brpnsted sites could not be determined because the contribution from these sites could not be studied independently. 

This configuration has been developed specifically to meet the high tonnage demands of basic chemicals such as ammonia (50 to 100 tons/h). hi this reactor proposed by Haldor Topspe, the catalyst is placed between coaxial cylinders, and the gas flows either from or to the center, as shown in Figure 11.30. The pressure drop is low, since only a short length of the catalyst bed is used. Based on several studies (Raskin et al., 1968a, b Hlavacek and Kubicek, 1972 Hlavacek and Vortuba, 1977 Strauss and Buddie, 1978 Calo, 1978 Balakotaiah and Luss, 1981), some useful conclusions can be drawn ... 

TPD of basic probe molecules is a method which is often used for the analysis of zeolitic acidity [24], In a parallelized implementation [25] of this technique, the samples to be studied were placed in a parallel channel reactor-body built analogous to the one described by Hoffmann et al. [26], By means of a multiport valve, the effluent from each channel could be switched to a mass spectrometer which was used for the analysis of the desorbed gas. In a typical experiment, after conditioning of the samples and adsorbing ammonia, a temperature ramp was started and in a sequential manner the effluent of each catalyst was fed into the mass spectrometer. Flushing and analysis times per channel were 8 s, so that all 10 samples could be analyzed in somewhat more than one minute. This proved to be sufficient to obtain well resolved TPD curves at a heating rale of 10 K/min. The recorded data corresponded well to curves measured with conventional setups. 

This type of reaction requires a complex, multifunctional catalyst with acid and hydrogenating properties. In a previous work we showed that these properties and hence the activity and the selectivity of the catalyst depended very much on the support and on the various promoters of copper which was chosen as a basic metallic element (1, 2). Furthermore the stability of the catalysts also depends largely on their composition and of certain products of the reaction such as water and ammonia (3). We have therefore studied the modifications of the bulk and surface compositions as well as those of the adsorption properties of supported (alumina or graphite) or promoted (barium) copper-chromium... 

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