P. H. Emmett

Exchange between N230 and N228 over Iron Catalysts

The rates of exchange between N228 and N230 obtained on doubly‐ and singly‐promoted iron catalysts is of the right order to be accounted for by assuming that all nitrogen evaporating from the surface of the catalyst is completely equilibrated with respect to the nitrogen isotope exchange. Large concentrations of hydrogen (50 percent H2 in N2) markedly accelerate the reaction. Small traces of surface oxides poison the iron catalysts severely for the isotope exchange.

The exchange of H218O with the oxygen of promoters on the surface of iron catalysts

Abstract The oxygen content of promoter oxides or other metallic oxide on the surface of iron synthetic ammonia catalysts has been estimated by a method involving equilibration with a known quantity of H 2 18 O in hydrogen at 450 °C. The results indicate a surface coverage by promoters of about 60% for a catalyst containing 1.06% Al 2 O 3 and 0.52% K 2 O. With reasonable assumptions in regard to the cross sectional area of oxygen ions the coverage agrees with that estimated from the chemisorption of carbon monoxide at −195 °C on the same catalyst. A pure iron catalyst revealed only a 1.2% coverage with oxygen after extended reduction at 450 °C.

Dehydrogenation—The first step in the cracking of isopentane over silica-alumina cracking catalysts

Abstract Earlier work has shown that at low conversions, dehydrogenation is the main primary reaction when isopentane is passed over a silica-alumina catalyst, and that the resulting pentenes largely determine the products and kinetic parameters of cracking (Garten, Ph.D. Thesis, Johns Hopkins University, 1967) . Results reported here indicate that the dehydrogenating activity of the catalyst is intrinsic and not the result of trace impurities. Further, the dehydrogenation activity is not related to the ability of the catalyst to hydrogenate ethylene in a hydrogen-ethylene mixture. The latter activity appears to be the result of catalyst impurities, probably iron, and is easily poisoned by hydrogen sulfide. These observations agree with the conclusion from previous work (Garten, 1967) that at least for isopentane cracking, the traditional “secondary reaction” role accorded to the corresponding olefins should be supplanted by considering dehydrogenation of the paraffinic feed as the major primary reaction of cracking, the breaking of the carboncarbon bond being a subsequent step to dehydrogenation.

Measurement of Carbon Black Particles by the Electron Microscope and Low Temperature Nitrogen Adsorption Isotherms

Electron micrographs and nitrogen adsorption isotherms have been compared on six commercial carbon blacks as methods for obtaining particle size and surface area values of finely divided materials. Good agreement between the two procedures was obtained for four of the backs: Grade 6, P 33, acetylene black, and lampblack. For two blacks known to be porous, Mogul and after‐treated lampblack, the areas, as measured by the nitrogen isotherms, were 5 to 7 times as large as one would calculate from the electron microscope results.

The catalytic hydrogenation of ethylene on nickel-copper and nickel-gold alloys

Abstract The rate of ethylene hydrogenation on copper-nickel alloy films in the temperature range 0 ° to 21 °C has been measured. The films were prepared by successive deposition of copper and nickel by the usual film-forming procedures followed by sintering the films in 5 cm of hydrogen at either 300 ° or 500 °C. The activity per unit area of film increases to a value 7 to 15 times as great for a catalyst containing 10% to 20% Cu as for pure nickel. Similarly, catalysts containing 5% to 20% nickel are as much as eight times as active as pure nickel. A minimum of activity with composition is found in the 25% to 35% nickel region, where the activity is about the same as on pure nickel. X-Ray data show that films homogenized by heating to 500 °C in a few cm of hydrogen form an alloy containing about 60% copper; the excess of nickel or copper present gives a diffraction pattern for the pure metal. Gold-nickel alloys containing 15% and 55% gold, respectively, have rates only about one-tenth as great as that of pure nickel. The apparent energies of activation for the reaction over the copper-nickel alloys vary with composition in the range 9 to 12 kcal/mole; those for the two gold-nickel alloys are about 4 kcal. The reaction rate is first order with respect to hydrogen and independent of ethylene for the copper-nickel alloys and for pure nickel; it is first order with respect to both hydrogen and ethylene for copper.

Use of controlled oxidation to increase the surface area of coal: Application to a bituminous and a semi-anthracite coal

Abstract This Paper supplements previous work on the use of controlled oxidation to increase the surface area of coal by examining the effects of different temperatures of treatment and different ranks of coal. The work on an hvA bituminous coal showed no increase in the area by nitrogen when the oxidation was carried out at 375 °C, but at least a 72-fold increase at 400 °C. The increase in surface area measured by nitrogen adsorption for two other coals (a semi-anthracite and an hvC bituminous coal) similarly oxidized, varied from 3 to 20-fold, depending on whether comparison is made with the values for the raw coal or with values obtained after heating to 400 °C in nitrogen. Measurements made on the stability of the increased surface as a function of time showed that the newly created surface disappeared at rates as high as 30% per month.

Interaction of nitrogen and carbon monoxide on iron synthetic ammonia catalysts

Abstract The inhibitive effect of nitrogen chemisorption on the adsorption of carbon monoxide has been studied over a singly and a doubly promoted iron synthetic ammonia catalyst. The adsorption of nitrogen at 450 °C did not decrease the amount of carbon monoxide chemisorption capable of taking place at −183 ° or −195 °C. On the other hand, in the temperature range 130 ° to 300 ° the inhibition increased with a decrease in temperature and corresponded, at the lowest temperature, to a decrease of as much as 0.7 cc of carbon monoxide chemisorption per cc of chemisorbed nitrogen. The results seem to indicate that in the temperature range 130 ° to 300 °C a considerable portion of the chemisorbed nitrogen on iron synthetic ammonia catalysts is held as nitrogen molecules, or NN or NN groups, whereas at temperatures of about 450 ° it is held on the surface primarily in the atomic form.

The Use of Isotopic Tracers in Studying Catalysts and Catalytic Reactions

Abstract Nonradioactive tracers such as deuterium, 18O, 15N, and 13C and radioactive tracers such as tritium and l4C have been used extensively for studying the properties of catalysts and the details of catalytic reactions. In the present paper an attempt will be made to show how the uses that have been made of isotopes in catalysis can be divided into one of three categories accordingly as they are concerned with (1) the study of the chemisorption of molecules on a catalyst surface and the nature of the catalyst surface; (2) the measurement of the extent to which the atoms from the structure of the solid catalyst take part in a catalytic reaction and become a part of the product; and (3) the details of the mechanism by which the catalytic reactions take place on the catalyst surface. These three categories will now be discussed and illustrated.

Fifty Years of Progress in the Study of the Catalytic Synthesis of Ammonia

The catalytic synthesis of ammonia developed in Germany in the 1908 to 1913 period has probably been studied more extensively during the past 50 years than any other catalytic reaction. Research endeavors include the development of a method for measuring the surface area of the catalysts; a study of the adsorption of both hydrogen and nitrogen by the iron catalysts; a phase-rule study of the formation of nitrides of iron from ammonia-hydrogen mixtures; a study of the distribution of promoters on the catalyst surface; methods for estimating the fraction of adsorbed nitrogen present in the molecular form; and estimates from infrared spectroscopy, from LEED measurements, and from ion-emission spectroscopy as to the path followed during synthesis and the catalyst planes important in the synthesis. Recently, revolutionary nonferrous catalysts severalfold more active than standard iron catalysts have been prepared by Ozaki. These throw new light on the mechanism of the catalytic synthesis of ammonia.

Enlargement of the micropores of a caking bituminous coal by controlled oxidation

Abstract In a study of the enlargement of pores of coals it has been found that treatment of a bituminous coal (PSOC No. 371, from the Pennsylvania State University Coal Section) with a 5:95 O2:N2 stream 4 h at 400 °C increases the surface area as measured by nitrogen adsorption at 77K by a factor of at least 50 to a value 52 m2 g−1. The increase in pore size was accompanied by a 9.7% weight loss. Simultaneously, the area as measured by carbon dioxide at 195K increased from 61 to 136 m2 g−1 and that measured by carbon dioxide at room temperature increased from 125 to 237 m2 g−1. Attempts to enlarge the pores by oxidation with hydrogen peroxide or ozone were unsuccessful. A Pittsburgh coal subject to a small percentage of oxygen in nitrogen or steam at 300 to 400 °C showed a surface area as measured by nitrogen adsorption of less than 1 m2 g−1 both before and after such pretreatment. This same coal with a 5:95 O2:N2 stream for 4 h at 450 °C showed a surface area of 110 m2 g−1 measured by nitrogen adsorption at 77K.