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CONFERENCE ON ELECTRONIC PHENOMENA IN ADSORPTION AND CATALYSIS

From April 16 to 19, 1954, the “Conference on Electronic Phenomena in Catalysis and Adsorption” was held at the Institute of Physical Chemistry of the Academy of Sciences of the USSR.

The work of the conference showed that at the present time the electronic direction in catalysis is attracting the attention of broad circles of chemists and physicists and is one of the leading and most promising directions in the modern theory of catalysis.

At the conference, theoretical and experimental works of Soviet scientists, carried out in scientific institutions of Moscow, Leningrad, and Kiev, were reported. These works represent the principal directions in the study of electronic phenomena in catalysis and adsorption. More than 200 scientific workers took part in the conference, representing 35 institutions working in the USSR in the field of catalysis.

The conference was opened with an introductory report by Corresponding Member of the Academy of Sciences of the USSR S. Z. Roginskii (Institute of Physical Chemistry, Academy of Sciences of the USSR), “Electronic Phenomena in Catalysis.” Having briefly characterized the history of the electronic direction in catalysis, the founder of which was L. V. Pisarzhevskii, S. Z. Roginskii pointed out that only with the development of quantum mechanics did the prerequisites appear for constructing a serious electronic theory of adsorption and catalysis. The speaker further noted that in the USSR this direction is being successfully developed experimentally and theoretically by F. F. Vol’kenshtein in the catalysis laboratory of the Institute of Physical Chemistry of the Academy of Sciences of the USSR as applied to semiconductor catalysts, which are one of the most important groups of catalysts. However, for metals there is no electronic theory of adsorption and catalysis, which is a serious gap in the work of our theoreticians.

S. Z. Roginskii also noted that the connection between experimenters and theoreticians is still weak and that, in general, there is clearly an insufficient number of experimental works on the mechanism of catalysis and chemisorption on ionic crystals and semiconductors. A weak aspect of the work of our theoreticians, in the speaker’s opinion, is also the insufficient use of the modern theory of molecular structure. An undoubted merit of the theory is the development of the problem of the heterogeneity and activity of the surface, consideration of modification, and so on. Speaking about experimental work, the speaker noted that the nature of the participation of electrons of a solid in electronic and ionic transitions has been insufficiently studied. There is an acute lack of systematic data on the electrical state of the molecules of reacting substances on the surface. In general, the study by direct methods of the types and strengths of bonds and of the state of molecules on the surface of contacts is only beginning to develop (the school of Academician A. N. Terenin).

Electronic theory of catalysis (the work of F. F. Vol’kenshtein) has by now yielded many valuable results; however, a number of central questions in this field (the principles governing the selection of catalysts, the nature and role of intermediate labile forms in catalysis, etc.) still await resolution. All this requires a considerable expansion in the volume and scope of work—above all experimental work—the formulation of systematic experiments on the effect of various types of radiation on the catalyst, the use of magnetic methods, the development of the electron-emission line of research, etc. It is also necessary to study the electronic mechanism of the action of organic catalysts.

Touching on unclear and debatable questions, S. Z. Roginskii noted, as deserving special attention, the reasons for the far-reaching similarity in the adsorption and catalytic relation between metals and semiconductors despite enormous differences in the number of free electrons; the interrelation of electronic bulk and surface properties and methods of passing from readily studied bulk properties to little-studied surface properties; the prospects for influencing a catalyst by external radiation; the types of bonds in chemisorption; and the electrical state of the simplest molecules on the catalyst surface as a whole and at active points.

S. Z. Roginskii indicated that it is absolutely necessary to involve in work in the field of electronic phenomena in catalysis a large number of experimental physicists, especially those working in the study of electrical and magnetic properties of solids, in particular semiconductors. Successful development of research in this direction requires the establishment of the closest contact between physicists and chemists working in this field.

The reports presented at the conference may, by subject matter, be divided into several groups.

1. GENERAL QUESTIONS OF THE THEORY OF CATALYSIS

In the report of Doctor of Physico-Mathematical Sciences F. F. Vol’kenshtein (Institute of Physical Chemistry, Academy of Sciences of the USSR), “Some Questions of the Electronic Theory of Catalysis on Semiconductors,” the principal results of a number of the author’s theoretical works were presented.

The speaker showed that free electrons and holes, present in a certain concentration on the surface of a semiconductor, may be regarded as free valences (positive and negative, respectively).

These free valences possess a number of specific properties: they wander over the surface, are capable of being generated and disappearing, etc. The chemical adsorption of free atoms and radicals on the surface of a semiconductor is then investigated. It is shown that three types of bond are possible for an adsorbed atom with the surface: “weak” homopolar, “strong” homopolar, and ionic. In the first two cases, the valence of the adsorbed atom is saturated by a surface valence; in the first case it remains free, and the adsorbed atom represents a “heterogeneous” radical. Depending on the bond with the surface, the reactivity of the adsorbed atom changes. Thus, an atom in the state of a “strong” homopolar bond is less reactive than in the state of a “weak” bond. Transitions are possible between the various states of the adsorbed atom, and their mechanism was investigated by the speaker.

Equilibrium is characterized by a definite content of the various possible forms of adsorption. External influences on the crystal (change of temperature, introduction of impurities) lead to a definite shift of the equili-

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... novation, i.e., to a change in the relative content of the various forms of adsorption and thereby to a change in the reactivity of the adsorbed atoms.

The conclusions set forth above are based on quantum-mechanical calculations carried out by the author for the adsorption of an individual atom on a semiconductor crystal. The results obtained are generalized qualitatively to the case of adsorption of a saturated molecule.

The free valence of the surface leads to rupture of the valence bond inside the molecule. As a result, either dissociation of the molecule occurs, or, if the molecule has several bonds, its conversion into a heterogeneous radical. The adsorbed molecule, converted into a radical, thereby acquires increased reactivity.

In the concluding part of the report, F. F. Vol’kenshtein considered a possible mechanism of heterogeneous reactions of various types in which the process is carried out and controlled by the free valences of the surface. The catalyst acts in the role of a special “polyradical.” Such a conception of a crystalline catalyst brings heterogeneous catalysis closer to homogeneous kinetics.

The report of Cand. Chem. Sci. V. V. Voevodskii (Institute of Physical Chemistry, Academy of Sciences of the USSR) was devoted to chain mechanisms in heterogeneous catalysis. The speaker pointed out that analysis of experimental data leads to the conclusion that, during the transformation itself, active intermediate compounds exist on the catalyst surface which, in their properties, are very close to homogeneous free radicals. F. F. Vol’kenshtein arrived at the same conclusions on the basis of a theoretical consideration of the properties of solids. If the possibility of the existence of heterogeneous radicals is assumed, then it is also necessary to take into account the possibility of the existence of heterogeneous chain reactions, i.e., processes in which, between the elementary act of formation of a free valence on the surface and the reaction of its destruction, a considerable number of molecules of the final substances have time to be formed.

V. V. Voevodskii further indicated that chain conceptions make it possible to generalize anew a number of propositions of previously existing theories. With the aid of chain schemes, analogous to chain schemes in homogeneous processes, one can explain the direction of a large number of heterogeneous processes.

The application of chain conceptions makes it possible to propose new approaches to the analysis of the mechanism of catalytic processes, connecting the latter with the elementary stages of initiation and termination of chains.

The analogy between heterogeneous and homogeneous chain processes makes it possible to consider that the high rates in both cases are due to the partial use, in the course of the process, of the energy released in the formation of the final substances in the form of the chemical energy of active intermediate compounds—free radicals. The speaker noted that at present there are only indirect indications of the existence of heterogeneous chains. Therefore it is urgently necessary to carry out experiments to test chain conceptions in catalysis.

In the report of S. Z. Roginskii, “The Electronic Mechanism of Oxidation-Reduction Catalysis,” results were presented which had been obtained through the application of electronic conceptions to the solution of the important problem of the selection and mechanism of action of catalysts for oxidation-reduction reactions. The first part of the report was devoted to the regularities of catalyst selection. Contact reactions are divided into two major types: oxidation-reduction reactions and acid-base reactions; next, the regularities of selection and the electronic properties of catalysts for reactions were examined in detail.

of the first type. Special attention was devoted to the role of transition elements in oxidation-reduction catalysis.

In the second part of the report the mechanism of oxidation-reduction catalysis is considered. A number of concrete schemes are proposed for certain reactions (isotopic exchange in solutions, catalytic decomposition of H$_2$O$_2$, etc.).

In conclusion the speaker noted that electronic concepts do not annul such achievements in catalysis as the ideas concerning the existence of definite geometrical and energetic conditions, the nature of the active surface, and a number of other propositions, but make it possible to deepen and further develop the theory of these questions.

The report “On the possible role of a donor-acceptor bond in heterogeneous catalysis” was delivered by Doctor of Physical and Mathematical Sciences I. D. Sokolov (Institute of Physical Chemistry, Academy of Sciences of the USSR). The speaker noted that a donor-acceptor bond can, in certain cases, be responsible for the adsorption of molecules on solid surfaces. A donor-acceptor bond can influence a heterogeneous reaction, facilitating the ionization of reacting molecules. It is also possible that donor-acceptor interaction with active centers of the surface takes place not only in the case of stable molecules, but also in the case of activated complexes of heterogeneous reactions.

The theoretical treatment shows that for reactions accompanied by the rupture of electron pairs, owing to donor-acceptor interaction with the surface the activation energy of the heterogeneous reaction must decrease and, consequently, the surface will catalyze the reaction.

One of the conclusions of the theory is the necessity of geometrical correspondence between the structure of the reacting molecules and the structure of the active surface.

In conclusion the speaker pointed to the need for experimental verification of the theory set forth.

A number of interesting contributions were made in the discussion. A. I. Krasilshchikov reported on experiments concerning the influence of an electric field on the rates of heterogeneous reactions, which indeed should be observed from the point of view of the electronic theory developed by F. F. Vol'kenshtein. Such an effect was found for the reaction of combination with hydrogen on silver, platinum, and palladium.

In the contributions (V. V. Voevodskii, S. Z. Roginskii, A. A. Balandin, N. N. Semenov, S. Yu. Elovich, V. A. Roiter, V. A. Roich-Bruevich, and others), the principal questions of the electronic theory of catalysis were sharply discussed.

2. THE INFLUENCE OF ILLUMINATION ON THE ADSORPTIVE CAPACITY OF SOLIDS

Academician A. N. Terenin (State Optical Institute) delivered the report “Liberation of adsorbed gases from metals and semiconductors and their adsorption under the action of light.”

Illumination of a gas—solid-surface system, depending on the nature of the system and on the wavelength of the light, leads to the following processes.

a) Photodesorption of an unchanged molecule was observed when conditions existed for complex formation on the surface (for example, I$_2$/TiJ, CO/NiSO$_4$) or surface compounds were formed. The specific nature of the process does not allow it to be ascribed to the simple thermal action of the absorbed light.

b) Photosorption caused by illumination of the surface of a solid in the region of wavelengths absorbed by it was not observed for metals,

besides those cases in which photodissociation of the gas and the effect of “cleaning” of the atoms and radicals formed occur.

c) Photodecay of gas molecules adsorbed on a solid has been observed repeatedly. In this case the region of active wavelengths is shifted both toward smaller and toward larger quanta in comparison with the photodissociation of gaseous compounds. A change is also observed in the sensitivity of the adsorbent as a function of its surface treatment.

d) A photoreaction of a solid body with vapor molecules adsorbed on its surface is also observed.

In the work of A. N. Terenin and E. K. Putseiko, “The Influence of Gases and Vapors on Photoelectric Processes in Zinc Oxide and Other Semiconductors, Measured by the Condenser Method,” the photo-emf of porous ZnO was investigated.

A high sensitivity of electronic processes to the presence of foreign gases was shown. This indicates the surface course of electronic processes.

Comparison of the results for the photoeffect with the results of measurements of the influence of oxygen, water vapor, and ethane on the photoluminescence of ZnO under vacuum conditions shows that the change in the photoeffect is reproduced in changes of luminescence with the opposite sign. The observed phenomena fit into the idea of the appearance, as a result of adsorption, of surface levels of conduction electrons that are essential for the photoelectric properties of ZnO.

In the work of Doctor of Chemical Sciences Ya. P. Shchekochikhin and Candidate of Chemical Sciences I. A. Myasnikov (Karpov Institute of Physical Chemistry), “Desorption of Oxygen from Zinc Oxide under the Action of Light and Its Influence on Photoconductivity,” in order to clarify the nature of the bond of oxygen adsorbed on the surface of ZnO, the action of ultraviolet light on the electrical conductivity of ZnO in the presence of oxygen at various pressures and under various temperature conditions was investigated.

It was established that, upon illumination with ultraviolet in the region of the intrinsic absorption of the ZnO lattice, photodesorption of oxygen occurs. Temperature treatment of ZnO shifts the maximum sensitivity toward the long-wavelength part of the spectrum and diminishes the effect. From the data obtained, the authors conclude that the influence of oxygen on the electrical conductivity of ZnO is due to the formation of surface oxygen compounds.

V. I. Veselovskii and Candidate of Chemical Sciences D. M. Shub (Karpov Institute of Physical Chemistry) presented a report, “The Mechanism of Photosensitized Formation of Hydrogen Peroxide by Zinc Oxide and the Fluorescent Properties of Zinc Oxide.” The experimental data obtained in this work indicate that, under the action of optical radiation on the system suspension ZnO + aqueous NaOH solution, photoelectrochemical formation of hydrogen peroxide is observed; at the same time, a necessary condition for the appearance of peroxide is the presence of oxygen in the solution.

In the work, simultaneous study was carried out of the photochemical activity and fluorescent properties of ZnO in the presence of oxygen and nitrogen. A definite connection was established between the fluorescent and photosensitizing properties of ZnO. A parallelism is also observed in the change of ZnO activity in the reaction of H₂O₂ formation and in the quenching of fluorescence by oxygen.

In conclusion, the authors propose a staged mechanism for the reaction of H₂O₂ formation.

The report by N. I. Barshchevskii and L. A. Nikolaev (MIIT) was devoted to the features of the structure of active centers in photocatalysis.

It was established that heavy-metal ions introduced into the zinc oxide lattice transform it into a powerful photocatalyst. Ions of heavy metals,

metals enter into the composition of the active center of the photocatalyst, creating a specific arrangement of energy levels favorable for photocatalysis.

The authors consider that the active center is probably dipolar: it includes regions in which bleaching occurs, and regions necessary for catalysis. In addition, the active centers are labile formations with an irregular and nonuniform structure.

The speakers assume that on the surface of the photocatalyst there are at least three types of regions: a regular zinc oxide lattice, sites where activator ions are located, and regions that surround the sites of these defects.

The last of the works of this group is the report by A. A. Krasnovsky (Institute of Biochemistry, Academy of Sciences of the USSR), “Some Questions of Photocatalysis.” The report presents a number of results obtained by the author in recent years. The photosensitizing action of ZnO and TiO₂ for a series of organic reactions is noted.

Further, the author analyzes in detail the elementary mechanism of the photochemical formation of hydrogen peroxide on zinc oxide.

The author proposes the following scheme:

$$ \mathrm{ZnOH}^{+} + h\nu \to \mathrm{ZnO}^{+} + \mathrm{H} $$

$$ \mathrm{ZnO}^{+}\cdot \mathrm{H} + \mathrm{O}_{2} \to \mathrm{ZnO}^{+} + \mathrm{H}_{2}\mathrm{O} $$

etc.

The report also gives results on the influence of light on a number of catalytic reactions.

Speaking in the discussion, F. F. Volkenshtein pointed out that the experimental facts presented in the reports of A. N. Terenin, I. A. Myasnikov, and S. Ya. Pshezhetsky fit within the framework of the electronic theory of catalysis and, to a certain extent, confirm it. V. I. Lyashchenko reported on experiments concerning the influence of adsorption on the photoconductivity of a number of semiconductors.

A number of interesting considerations regarding the experiments of A. N. Terenin were expressed by L. N. Kurbatov (Naval Medical Academy, Leningrad), A. V. Kiselev (Institute of Physical Chemistry, Academy of Sciences of the USSR), V. V. Voevodsky, and S. Z. Roginsky.

3. RELATION BETWEEN ELECTRICAL CONDUCTIVITY AND CATALYTIC ACTIVITY

The report “The Influence of Methods of Preparation on the Catalytic Activity and Conductivity of Zinc Oxide” was presented by Doctor of Chemical Sciences G. K. Boreskov and K. I. Matveev (Physico-Chemical Institute named after Karpov). The work aimed to clarify: 1) the influence of the method of preparing a semiconductor catalyst of constant chemical composition on its electronic structure and catalytic activity; 2) changes in the electronic structure under reaction conditions; 3) the relation between the concentration of free electrons in the semiconductor and its catalytic activity.

Various ZnO samples were compared in terms of their catalytic activity in the decomposition reaction of methyl alcohol. To study the electronic structure, electrical conductivity was measured.

The data obtained show that the initial ZnO samples are typical semiconductors. However, under reaction conditions they were degenerate semiconductors. Changes in the electronic structure of the contact occurred under the action of the reducing medium, which took place

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under the conditions of the catalytic reaction. The catalytic activity of all samples became noticeable only when they had high conductivity, i.e., differed from the initial ones by high concentrations of free electrons. The changes in catalytic activity upon reduction were comparable with changes in the concentration of free electrons in the samples. Under the conditions of the catalytic reaction, the electronic structure of the contacts changed so strongly that its differences associated with the method of preparation could no longer be noted.

The results obtained show that, by varying the methods of preparation, without changing the chemical composition of the contact, it has not been possible to change substantially either the catalytic or the electronic properties of the samples under reaction conditions.

In the work “Investigation of the relationship between the catalytic and semiconducting properties of zinc oxide” (S. Ya. Pshezhetskii and I. A. Myasnikov), the activity of a ZnO catalyst with respect to the dehydration reaction of isopropyl alcohol in acetone was measured in an atmosphere of an inert gas (nitrogen) and a reducing agent (hydrogen) in the presence of small amounts of oxygen; the electrical conductivity was measured in parallel. The experiments were carried out in the temperature range 250–390° C. A correspondence was established between the change in the activity of the contact and its electrical conductivity, related to the chemisorption of oxygen. The results show that in this case the changes in catalytic activity and in electrical conductivity have one and the same cause. However, as the authors note, an unambiguous connection between these two phenomena still does not follow from this.

The results of the work “Change in the work function of copper oxide upon adsorption of molecules and in a catalytic reaction” were reported by Candidate of Physico-Mathematical Sciences V. I. Lyashenko. The work was carried out by him jointly with I. I. Stepko at the Institute of Physics of the Academy of Sciences of the Ukrainian SSR. The influence of the catalytic oxidation of carbon monoxide and of the adsorption of the gases participating in the reaction on the change in the electron work function and conductivity of thin layers of copper oxide was studied. The work function was measured by means of a vibrational electrometer constructed in the laboratory. The work function in vacuum, oxygen, and CO remained unchanged up to a temperature of 180° C (the temperature at which the reaction begins). In the case of a gas mixture, when the catalytic reaction set in, the work function changed sharply (at the same time there also occurs a break in the graph \(\ln I = f(1/T)\), where \(I\) is the current, \(T\) the absolute temperature). On inactive samples of CuO the reaction did not proceed, and the work function and conductivity did not change.

It was established that the change in the work function and current is caused by electron exchange during the catalytic reaction, and not by the appearance of carbon dioxide.

In the report by F. F. Volkenshtein and V. B. Sandomirskii (Institute of Physical Chemistry, Academy of Sciences of the USSR), questions of the relation between the catalytic properties of the surface of a semiconductor and its bulk electronic properties were considered theoretically. It was shown that the establishment of electronic equilibrium between the surface and the bulk of a crystal leads to a relation between the concentration of free valences on the crystal surface and the properties of the bulk. Two limiting cases were analyzed: a “sufficiently thin” and a “not too thin” crystal. In the first case, the concentration of free valences and the reactivity of adsorbed atoms do not depend on the properties of the bulk, but depend on the filling of the surface by adsorbed atoms or molecules. In the second case, both factors have an effect.

Adsorption on the surface of a crystal changes the concentration of electron gas inside a crystal of sufficiently small dimensions and, consequently, affects its electrical conductivity.

B. J. Bonch-Bruevich, who spoke in the discussion, highly praised the work reported by V. I. Lyashenko and I. I. Stepko.

S. Yu. Elovich noted that F. F. Vol'kenshtein had long ago theoretically predicted: the dependence of electrical conductivity on catalytic activity, the effect of adsorption on electrical conductivity, the effect of illumination on adsorption, etc. The experimental results reported to the present conference confirm this theoretical prediction and attest to the great promise of the electronic theory of catalysis developed by F. F. Vol'kenshtein.

A number of comments concerning the experimental papers presented were made by S. Z. Roginskii.

F. F. Vol'kenshtein pointed out a number of consequences of the electronic theory of catalysis that still require experimental verification.

In his concluding remarks S. Ya. Pshezhetskii, answering questions, indicated that he considers the electronic theory of catalysis developed by F. F. Vol'kenshtein to be very promising.

4. THE NATURE OF THE ACTIVE SURFACE

Candidate of Chemical Sciences G. M. Zhabrova (Institute of Physical Chemistry, Academy of Sciences of the USSR) gave a report entitled “Radiochemical Study of the Microchemistry of the Surface of a Zinc-Oxide Catalyst.”

The method of radioactive isotopes makes it possible to monitor the content of microimpurities in a catalyst. The reaction of decomposition of isopropyl alcohol was investigated; it can proceed in the directions of dehydrogenation and dehydration.

It was established that, in accordance with ideas about the electronic type of the dehydrogenation process and the acid–base type of the dehydration process, acid additions sharply shift the selectivity of the catalyst’s action toward dehydration. The same effect is exerted by acidic salts and by salts hydrolyzing in solution with an acid reaction. The addition of a neutral sulfurous-acid sodium salt did not affect the selectivity of ZnO, whereas the addition of NaOH increased dehydrogenation.

A study of the adsorption capacity of the indicated electrolytes on ZnO showed a certain parallelism with catalytic action.

An attempt was made to explain the phenomena described from the standpoint of the electron-chemical concept of the active surface of catalysts.

Candidate of Chemical Sciences N. P. Keier (Institute of Physical Chemistry, Academy of Sciences of the USSR) delivered a report, “Study of the Inhomogeneity of the Active Surface of Certain Semiconductors by Isotopic Methods.”

The application of the differential isotopic method, developed by S. Z. Roginskii, in combination with the study of the exchange of adsorbed molecules and molecules from the gas phase and the study of adsorption and desorption makes it possible to distinguish a pseudohomogeneous surface from a truly inhomogeneous surface. Investigation of the active surface of nickel oxide with the aid of labeled C^14 acetylene indicates inhomogeneity with respect to activation energies and heats of adsorption. An analogous investigation leads to the presence of two forms of ethyl alcohol on the ZnO surface and points to the pseudohomogeneous character of the bonding of ethyl alcohol at room temperature.

The same conclusion was drawn as a result of studying the adsorption of ethyl alcohol on the surface of aluminum oxide.

The results of a number of works by the authors on the theory of chemical adsorption on semiconductors were presented in the report by Candidate of Physico-Mathematical Sciences V. L. Bonch-Bruevich (MEIS) and F. F. Vol'kenshtein.

The energetic inhomogeneity of the surface of most contacts is an experimentally established fact. The statistical theory of an inhomogeneous surface, developed by S. Z. Roginskii and his collaborators,

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while providing a convenient apparatus for describing processes occurring on such a surface, cannot, however, answer a number of questions connected with the properties of an inhomogeneous surface (the nature of adsorption centers, the physical causes of deviations of adsorption regularities from Langmuir’s, the physical origin of various “distribution functions”). Under certain conditions the role of adsorption centers is played by free electrons (and holes) of the lattice. Their number is regulated by the temperature and by the concentrations of impurities in the lattice and of adsorbed atoms. As can be shown in this case, the adsorption regularities may prove to be non-Langmuirian (on a homogeneous surface and when the force interaction between adsorbed molecules is neglected).

Structural defects of the surface may also play the role of adsorption centers; for them two types of bond with adsorbed atoms are possible. Since the number of bonds of either type is regulated by electronic equilibrium in the adsorbent, this also leads to a non-Langmuirian form of the isotherms. The same is observed when two types of bond are present on a “clean” surface.

The form of the isotherm on a homogeneous surface is not universal, but is a characteristic of the given system. In chemical adsorption the “distribution function” over heats of adsorption (and over activation energies) is not a characteristic of the adsorbent as such, but characterizes the properties of the adsorption system as a whole. In the apt expression of V. L. Bonch-Bruevich, the “distribution function” is not a permanent passport of the surface, but only its temporary certificate. Further development of the theory of an inhomogeneous surface must proceed by elucidating the physical nature and physical origin of one or another type of inhomogeneity.

In the discussion, A. A. Balandin dwelt on the report of G. M. Zhabrova and cited experimental facts obtained in his laboratory and confirming the results of the speaker.

G. K. Boreskov noted that the work of F. F. Vol’kenshtein and V. L. Bonch-Bruevich is of great interest. In his opinion, for most catalysts the action of regulating substances on the catalyst is very significant.

F. F. Vol’kenshtein dwelt on the present state of the theory of an inhomogeneous surface and noted that, in his opinion, further development of the theory of an inhomogeneous surface must proceed along the path of investigating the elementary mechanisms of adsorption processes and elucidating the physical nature of the active surface.

N. N. Kavtaradze reported the results of a number of experiments on adsorption on metals. S. Z. Roginskii made a number of critical remarks concerning the work of N. P. Keier.

The last two reports were devoted to questions of methods for the investigation of catalysts.

In the report by Candidates of Chemical Sciences O. V. Krylov and E. A. Fokin (Institute of Physical Chemistry, Academy of Sciences of the USSR), “On measuring the acid–base properties of a surface,” a method developed for measuring the basic properties of a surface was described. Whereas methods for measuring the acidic properties of catalysts exist, until recently there had been no way to measure the characteristics of the basicity of catalysts. The basic properties of a surface can be studied by means of the adsorption of acids. The most convenient substance for this purpose is phenol. The kinetics of adsorption and desorption of phenol at temperatures of 20–380° C and a constant pressure (0.1 mm Hg) were studied by the gravimetric method on acidic, basic, and amphoteric adsorbents: BeO, MgO, ZnO, CdO, CaO, Ca(OH)₂, Al₂O₃, SiO₂, and systematic aluminosilicate. At the same time the catalytic activity with respect to the decomposition reaction of isopropyl alcohol was measured. Ad-

the adsorption of phenol on all specimens, except the acidic ones, is very strong. On acidic catalysts phenol is readily desorbed during evacuation. The bond of phenol with the surface of strongly basic specimens is the strongest. The acidic properties of the same contacts were studied by the adsorption of pyridine. It proved that the order of the catalysts in terms of the strength of the bond of the adsorbed pyridine is, to some extent, the reverse of the order in terms of the strength of the phenol bond.

A comparison of the data shows that catalysts which adsorb phenol most strongly conduct the reaction predominantly toward dehydrogenation, whereas catalysts which adsorb pyridine most strongly conduct it toward dehydration. Thus the possibility has been demonstrated of developing an adsorption method for characterizing the quantity and quality of the basic properties of a surface.

In the report by Cand. Chem. Sci. B. P. Bering and V. V. Serpinskii (Institute of Physical Chemistry, Academy of Sciences of the USSR), “Change in the Adsorption of Nitrogen Vapors on Sodium Chloride Crystals by Means of Quartz Balances of High Sensitivity,” the construction of quartz microbalances is described. The operating principle of the microbalances is that weighing on microbalances with an accuracy of about \(1 \cdot 10^{-7}\) g replaces weighing on technical balances with an accuracy of \(1 \cdot 10^{-2}\) g. For this purpose the microbalances are optically linked with a differential photorelay suspended on technical balances. The deviation of the balances from the equilibrium position is measured by the change in the load on the pan of the technical balances required to return the photorelay prism to its initial position relative to the light beam.

The meeting adopted a resolution stating that the “reports presented and the discussion held helped to establish contact among scientists working in this field and made it possible to formulate a number of questions requiring further investigation. These include the establishment of quantitative regularities between the catalytic activity of semiconductors and their electronic characteristics.”

The necessity is emphasized of undertaking “work on the electronic mechanism of catalysis on metals and on the study of electronic phenomena in organic catalysis.”

It is also noted that the experimental studies reported are “in agreement with the theoretical concepts being developed in the catalysis laboratory of the Institute of Physical Chemistry, Academy of Sciences of the USSR.”

The attention of a number of scientific institutions is drawn to the need for broad development of work in the field of electronic phenomena in catalysis and for the participation of physicist-experimenters in such work. The participants in the meeting found it desirable to convene periodic conferences to discuss work in the field of electronic phenomena in catalysis and adsorption.

A collection of the proceedings of the meeting, containing the texts of the reports and transcripts of the discussion contributions, will be published at the beginning of 1955.

V. B. Sandomirskii
V. P. Smilga