STUDY OF THE EFFECT OF PRESSING ON THE ACTIVITY OF A METHANOL ZINC–CHROMIUM CATALYST

N. P. KURIN and D. F. PERMINOV

Numerous studies in the field of heterogeneous catalysis point to the enormous importance of the method of preparation for the activity of catalysts. Very often catalysts with an entirely identical chemical composition, but prepared by different methods, possess sharply differing activities [1].

In this connection we became interested in the question of whether it is possible to improve the catalytic properties of the zinc–chromium methanol catalyst currently used in industry by applying only such a physical method of action as pressing. During pressing, as a consequence of the increase in density, a number of important properties of the catalyst change, such, for example, as porosity, effective active surface, thermal conductivity, etc.; therefore one could expect in advance a change in its activity as well.

In the literature on the question of the effect of pressing on the activity of methanol catalysts there is only the work of Huttig, Kostelitz, and Kittel [2]. These authors found that the activity of ZnO, pressed in the form of zinc carbonate to a pressure of 5000 atm, increases almost threefold. As for zinc–chromium catalysts, the literature data are limited only to the report of Plotnikov, Ivanov, and Pospekhov [3], who, pressing the catalyst to an elevated pressure (300 atm), did not detect any detrimental effect of pressing on its activity.

In view of the above, the aim of the present work is to study the effect of pressing over a wide range of pressures on the activity of an industrial zinc–chromium catalyst.

Preparation of the catalyst and method of investigation

The finished industrial catalyst of composition ZnO. Cz₂O₃CrO₃ was ground in an agate mortar and screened through a sieve with 0.06 mm openings. The uniformly colored powder obtained in this way was moistened with distilled water and subjected to pressing at various pressures. The moistened powder was charged into a steel die A (Fig. 1), and with plunger B, using a hydraulic press, was compressed to the required pressure. In the first period of pressing (1–1.5 minutes), shrinkage of the briquette was observed, accompanied by a certain drop in pressure; therefore, during pressing, by feeding oil into the cylinder of the hydraulic press, the pressure was maintained at the desired level. After the shrinkage of the catalyst ceased, the pressure was reduced. The tablets obtained were dried at a temperature of 120°C for 4–5 hours, while their high mechanical strength was retained. The tablets were then crushed, and for the activity study the fraction having pieces of size from 1.5 to 2 mm was used. For preven-

to prevent contamination of the catalyst during pressing by iron and its oxides, which are contact poisons, the inner walls of sleeve A and plunger B were lined with brass. At 10,000 atm, the brass sleeve jammed against plunger B; therefore, in this case plunger A was made with a diameter equal to the diameter of sleeve A, and the surface of the catalyst was separated from the steel plunger by means of a brass disk.

Fig. 1

The activity of the catalyst treated in this manner was studied by the method of decomposition of methanol vapor at atmospheric pressure. In an apparatus developed by one of us [4], the study was carried out by the dynamic method, with accurate measurement of the amount of vaporized methanol passed through the catalyst under conditions close to isothermal. The study of the catalysts consisted of two periods: 1) the period of establishing a stationary state, evidently associated with the process of partial reduction of the catalyst; 2) the period of direct testing of activity.

The reduction of the catalysts began at 250°C and ended at the temperature of 100% decomposition of methanol vapor. The space velocity in the first period was equal to 600 volumes of methanol vapor (under normal conditions) per one bulk volume of catalyst per hour. The transition from one temperature to another during the reduction period was carried out in steps of 25°C after a stationary state had been established, characterized by constancy in the amount of noncondensable gaseous products formed and constancy in the amount of liquid phase condensed in the condenser. During the period of activity testing, some time was spent establishing the stationary state not only when passing from one temperature to another, but also when passing from one space velocity to another.

Results Obtained and Their Discussion

By the described procedure, 6 catalysts were prepared. The first of them was used without pressing; the others were subjected to pressing at 100, 1000, 2500, 5000, and 10000 atm. The activity of these catalysts was studied as a function of space velocity (420–2100) and temperature (250–375°C). The results obtained are collected in the tables below.

Table 1

Change in the weight of 1 ml of bulk volume of zinc–chromium catalyst as a function of pressing pressure

From Table 1 and Fig. 2 it is seen that, with increasing pressing pressure, the weight per unit bulk volume of the catalyst at first (up to 100 atm) increases rapidly, and then more slowly, reaching 1344 g/ml at 10000 atm, i.e., 1.73 times greater than the analogous value characteristic of the unpressed catalyst.

The duration of establishment of the stationary state during the reduction period practically does not depend on the pressing pressure, and at a methanol vapor space velocity of 600 for all temperatures (from 250 to 350°C in 25°C increments) amounts in total to 4–4.5 hours; in contrast to the zinc–copper catalysts previously studied by us [4, 5, 6], this catalyst very rapidly acquires its final activity.

Fig. 2

The results of the study of the activity of catalysts reduced in this manner as a function of space velocity and temperature are given in Table 2 and shown in Figs. 3–8.

Table 2

Percentage decomposition of methanol as a function of space velocity and temperature in the presence of zinc–chromium catalysts pressed at various pressures

(Continuation of Table No. 2)

Fig. 3. Dependence of the percentage decomposition of methanol on the space velocity and temperature in the presence of a zinc–chromium catalyst prepared without pressing.

Fig. 4. Dependence of the percentage decomposition of methanol on the space velocity and temperature in the presence of a zinc–chromium catalyst pressed at 100 atm.

Fig. 5. Dependence of the percentage decomposition of methanol on space velocity and temperature in the presence of a zinc–chromium catalyst pressed at 1000 atm.

Fig. 6. Dependence of the percentage decomposition of methanol on space velocity and temperature in the presence of a zinc–chromium catalyst pressed at a pressure of 2500 atm.

Fig. 7. Dependence of the percentage decomposition of methanol on space velocity and temperature in the presence of a zinc–chromium catalyst pressed at 5000 atm.

Fig. 8. Dependence of the percentage decomposition of methanol on space velocity and temperature in the presence of a zinc–chromium catalyst pressed at 10000 atm.

From the table and figures presented, it is evident that, with an increase in temperature and a decrease in space velocity, the degree of decomposition of methanol vapor in the presence of all the catalysts we studied increases.

Noticeable decomposition of methanol vapor with formation of noncondensable gaseous products in the presence of the unpressed catalyst and at a space velocity of 420 occurs at a temperature of 275°C. As for the pressed catalysts, decomposition is observed at a lower temperature (250°C).

The temperature of 100-percent decomposition of methanol vapor at a space velocity of 420 for the unpressed catalyst is 375°C; for the pressed catalysts the analogous value falls to 350°C; thus, pressing of zinc–chromium catalysts lowers the temperature of 100-percent decomposition.

The influence of the magnitude of the pressing pressure on the activity of the industrial zinc–chromium catalyst is clearly presented in Figs. 9–14.

Fig. 9. Dependence of the percentage decomposition of methanol vapors on the pressing pressure at various temperatures and a space velocity of 420.

Fig. 10. Dependence of the percentage decomposition of methanol vapors on the pressing pressure at various temperatures and a space velocity of 600.

Fig. 11. Dependence of the percentage decomposition of methanol vapors on the pressing pressure at various temperatures and a space velocity of 800.

Fig. 12. Dependence of the percentage decomposition of methanol vapors on the pressing pressure at various temperatures and a space velocity of 1200.

Fig. 13. Dependence of the percentage decomposition of methanol vapor on the pressing pressure at different temperatures and a space velocity of 1600.

Fig. 14. Dependence of the percentage decomposition of methanol vapor on the pressing pressure at different temperatures and a space velocity of 2100.

The data given in Table 2, as well as Figs. 9–14, indicate a strong effect of pressing on the activity of a unit of bulk volume of the zinc–chromium catalyst now used in industry. Namely, at all the temperatures and space velocities investigated, initially, with an increase in the pressing pressure up to 5000 atm, the catalytic activity increases, and with a further increase in the pressing pressure up to 10000 atm the activity decreases somewhat, remaining, in absolute magnitude, considerably higher than the corresponding value characteristic of the unpressed catalyst. A certain exception to the indicated regularity is the catalyst pressed at 2500 atm; namely, in this case, at temperatures of 325°C and below, a certain decrease in activity is observed in comparison with the activity of the catalyst pressed at 1000 atm, and thus on the curves, percentage decomposition \(= f(P_{\text{press.}})\), 2 maxima (1000 and 5000 atm) and 1 not very strongly expressed minimum (2500 atm) are observed.

Of all the catalysts studied by us, the catalyst pressed at 5000 atm has the greatest activity.

As Table 3 shows, in the temperature range 245–325°C the activity of a unit of bulk volume of the catalyst at 5000 atm, measured by the percentage decomposition of methanol, is greater than the activity of the unpressed catalyst by 3–6 times. If one confines oneself to pressing up to 1000 atm, i.e., to a pressure only slightly greater than that used for obtaining other industrial catalysts (e.g., for the conversion of carbon monoxide), then the activity under the indicated conditions increases by 1.3–2 times.

Table 4 gives the values of the quantity \(B\), indicating how many times the activity of a unit weight of catalyst pressed at a given pressure differs from the activity of the unpressed catalyst. The quantity \(B\) was calculated by the following equation:

\[ B=\frac{a_2 g_1}{a_1 g_2}, \]

where \(a_1\) and \(a_2\) are the percentages of methanol decomposition at the same temperature and space velocity in the presence, respectively, of the unpressed and pressed catalysts;

\(g_1\) and \(g_2\) are the weights, respectively, of the unpressed and pressed catalysts contained in 1 ml of bulk volume (Table 4).

Table 3

Ratio of the percentage decomposition of methanol observed in the presence of the pressed catalyst to the analogous value for the unpressed catalyst (A)

Table 4

Values of the quantity B, expressing the ratio of the percentage decomposition of methanol, referred to unit weight of the pressed catalyst, to the analogous value for the unpressed catalyst

From Table 4 it is seen that pressing, if it is limited to pressures on the order of 1000 atm, as a rule somewhat lowers the activity of a unit weight of catalyst. However, at higher pressures the activity of a unit weight of pressed catalyst becomes greater than the analogous value characteristic of the unpressed catalyst; thus, at 5000 atm and 275–375°C the increase in activity amounts to from 2 to 3.5 times.

Comparing the data of Tables 3 and 4, it may be noted that with an increase in the pressing pressure, the activity of a unit bulk volume of catalyst increases to a greater extent than is the case for a unit weight of catalyst.

This phenomenon can be explained by the fact that, with increasing pressing pressure, the catalyst surface available to the reacting gas per unit weight decreases.

It should be noted here that for the synthetic methanol industry, operating at high pressures, and with the low cost of the catalyst, the problem of increasing the activity of a unit bulk volume of catalyst is of greater importance, since this will make it possible to utilize the reaction volume of contact apparatuses to the maximum.

The composition of the gas, as an indicator of the degree of selectivity of action, for catalysts pressed at pressures above 1000 atm is characterized by the complete absence of methane and organic products absorbed by concentrated sulfuric acid. For catalysts pressed at pressures below 1000 atm, the methane content reaches 4% and that of organic products up to 3%. For all the catalysts investigated by us, the gaseous products of methanol decomposition contain 4–10% carbon dioxide, 10–30% carbon monoxide, and 59–84% (by volume) hydrogen; moreover, with increasing temperature a certain improvement in the composition of the gas is observed from the point of view of its approach to the composition characteristic of methanol decomposition according to the stoichiometric equation $\mathrm{CH_3OH = CO + 2H_2}$; in particular, the CO content increases somewhat, while $\mathrm{H_2}$ decreases.

Thus, from all that has been set forth above, it is seen that pressing, along with increasing mechanical strength, provides a new method for a considerable increase in the activity of a unit bulk volume of zinc–chromium methanol catalyst.

Taking into account the existing parallelism [7] between the activities of methanol catalysts for the forward and reverse reactions, it should be expected that the relatively high catalytic activity of pressed zinc–chromium catalysts is also retained for the direct reaction of synthesis of $\mathrm{CH_3OH}$ from hydrogen and carbon monoxide. The use of pressed catalysts will make it possible to intensify the operation of industrial contact apparatuses, and in this connection it is necessary to undertake the study of their activity at high pressure under laboratory conditions and on a pilot-plant scale.

As shown in our previous communications [4, 5, 6], the decomposition of methanol vapors in the presence of catalysts obtained by the reduction of zinc and copper sulfides proceeds according to an apparently zero order. Naturally, the question arises whether this order is also retained in the presence of the industrial zinc–chromium catalyst investigated by us. To answer this question, we calculated the rate constants of decomposition according to the integral kinetic equation already proposed earlier by one of us [4],

\[ K = V(1+\alpha)\frac{T}{273}\alpha, \]

where $K$ is the rate constant, $V$ is the space velocity,

\(T\)—absolute temperature and \(\alpha\)—degree of decomposition of methanol in fractions of unity.

The results of these calculations are given in Table 5, from which it is evident that, in the overwhelming majority of cases, within the limits of experimental error the constancy of the rate constants calculated at different space velocities (\(t^\circ C = \mathrm{Const.}\)), i.e., different reaction times, is fulfilled quite satisfactorily. Thus, the decomposition of methanol vapors

Table 5

Rate constants of the reaction of decomposition of methanol vapors in the presence of a zinc–chromium catalyst pressed at various pressures, calculated by equation (1)

Note: 1) in calculating \(K_{\mathrm{av}}\), the figures marked with an asterisk (*) were discarded; 2) the values of the figures in the rows marked ** were calculated by equation (2).

in the presence of the zinc–chromium catalysts investigated by us proceeds according to the law for a zero-order reaction. However, at elevated temperatures (350 and 375°C), in the presence of catalysts pressed at 100, 5000, and 10000 atm, the rate constants calculated for different space velocities do not remain constant, but increase systematically; thus, the decomposition ceases to obey zero order.

Taking into account the often observed decrease in adsorption with increasing temperature, it was natural to suppose that, under these conditions, the reacting substances would not completely cover the reaction-capable surface and, consequently, their concentration in the adsorption layer, where the decomposition itself actually takes place, begins to depend on the partial pressure in the gas phase; therefore the zero order of decomposition is violated. Assuming that, at elevated temperatures, decomposition proceeds according to a monomolecular law, and proceeding in the same way as was done in [4] in deriving equation (1), the integrated equation for the monomolecular process of methanol decomposition was obtained in the following form:

\[ K = V \frac{T}{273} (1+\alpha)\, 2.303 \log \frac{1}{1-\alpha} \tag{2} \]

The quantities entering equation (2) have the same meaning as in equation (1). We shall only point out that in equation (2) the time quantity \((t)\) has been replaced by the quantity proportional to it—

\[ \frac{1}{V \frac{T}{273}(1+\alpha)}. \]

The constancy of the rate constants calculated from equation (2), at different space velocities, for the above-indicated \(t\)-\(p\) values and catalysts, is fulfilled much better than was the case when using kinetic equation (1). Thus, on transition to elevated temperatures, the order of methanol decomposition approaches first order.

On the basis of the temperature dependence of the rate constant of methanol decomposition, expressed by the well-known Arrhenius equation

\[ \log K = -\frac{E}{2.303\,RT} + \mathrm{Const} \tag{3}, \]

the activation energies of the methanol decomposition process in the presence of all the catalysts investigated by us were calculated. The results of the calculations are given in Table 6.

Turning to the question of the mechanism of the process of decomposition of methanol vapors in the presence of the zinc–chromium catalysts investigated by us, it should be pointed out that, with an apparent zero order, the true order of methanol decomposition in the adsorption layer remains hidden; the zero order of decomposition indicates only such intensive adsorption of the reacting substance that the reaction-capable surface is almost completely covered by it, irrespective of its partial pressure in the gas phase.

Fig. 15.

Table 6

Values of the activation energy of the methanol decomposition process in the presence of zinc–chromium catalysts

phase; from the kinetic standpoint this leads to the absence of a dependence of the decomposition rate on the partial pressure of the reactant.

Dosa [8] found that the apparent order of methanol decomposition in the presence of zinc oxide is equal to zero; however, by studying the kinetics of the decomposition process as a function of the density of coverage of the reaction surface by the reacting substance, he was able to show that the true decomposition of methanol in the adsorption layer is monomolecular and consists of two consecutive reactions:

\[ \mathrm{CH_3OH \rightarrow CH_2O + H_2,} \]

\[ \mathrm{CH_2O \rightarrow CO + H_2.} \]

On the basis of the character of the straight line \(\log K = f\!\left(\frac{1}{T}\right)\), we came to the same conclusion regarding the mechanism of methanol decomposition in the presence of the zinc–copper sulfide catalysts studied previously by us [4, 5, 6].

It may be supposed that in the presence of pressed zinc–chromium catalysts the true order of decomposition in the adsorption layer is likewise monomolecular; however, the character of this monomolecular decomposition must undoubtedly be more complex. Indeed, for a number of catalysts (Fig. 15), for example, those pressed at 1000, 2500, and 10000 atm, there is a clearly expressed break in the straight line

\[ \log K = f\!\left(\frac{1}{T}\right), \]

with the branch corresponding to elevated temperatures being located at a smaller angle to the abscissa axis than is the case for the branch of lower temperatures. A similar picture apparently also holds for catalysts pressed at 100 and 5000 atm, with the only difference that the more gently sloping branch of the straight line

\[ \log K = f\!\left(\frac{1}{T}\right) \]

is observed at lower temperatures, which is confirmed by the deviation of the points toward a greater slope at a temperature of \(250^\circ\mathrm{C}\).

The presence of a downward-directed break in the straight line \(\log K = f\!\left(\frac{1}{T}\right)\) indicates decomposition of methanol by two simultaneously occurring parallel reactions, accompanied by the expenditure of different amounts of activation energy.

A similar course of the straight line $\log K = f\left(\dfrac{1}{T}\right)$ was observed by Norrish and Rideal [9] in studying the reaction of hydrogen with sulfur. They showed that in this case parallel reactions proceed simultaneously, one of them being a homogeneous reaction between vaporous sulfur and hydrogen, and the other a heterogeneous reaction between hydrogen and liquid sulfur. The presence of two parallel reactions (homogeneous and heterogeneous) is used by Boreskov and Illarionov [10], who recently investigated the reaction of oxidation of sulfur dioxide by nitrogen dioxide, to explain the same course of the straight line $\log K = f\left(\dfrac{1}{T}\right)$.

Taking into account the zero order of methanol decomposition, it may be asserted that the presence of two parallel reactions is not connected with the decomposition of methanol vapor in the gas phase, and that both parallel reactions proceed in the adsorption layer on the surface of the zinc-chromium catalysts investigated by us.

However, for an unpressed zinc-chromium catalyst the break in the straight line $\log K = f\left(\dfrac{1}{T}\right)$ is directed not downward but upward. Apparently, a similar picture will be observed in the region of elevated temperatures (above 350°C) also for pressed chromium-zinc catalysts, which is confirmed by a certain deviation of the points from the straight line $\log K = f\left(\dfrac{1}{T}\right)$ toward a greater slope. The upward-directed break in the straight line $\log K = f\left(\dfrac{1}{T}\right)$ indicates the presence of two consecutive reactions.

Thus, if the decomposition of methanol is considered over a wide temperature interval, then the straight line $\log K = f\left(\dfrac{1}{T}\right)$ will be characterized by the presence of two oppositely directed breaks, indicating the simultaneous occurrence of consecutive and parallel reactions.

In this connection, the following scheme of the process of methanol decomposition in the presence of zinc-chromium catalysts may be given as highly probable:

$$ 1.\quad \mathrm{CH_3OH}_{\mathrm{ads}} = \mathrm{CH_2O}_{\mathrm{gas}} + \mathrm{H_2}, $$

$$ 2a.\quad \mathrm{CH_3OH}_{\mathrm{ads}} = \mathrm{CH_2O}_{\mathrm{ads}} + \mathrm{H_2}, $$

$$ 2b.\quad \mathrm{CH_2O}_{\mathrm{ads}} = \mathrm{CO} + \mathrm{H_2}. $$

According to the proposed scheme, part of the methanol decomposes by reaction 1, and part by reactions 2a and 2b.

As is known, in the case of parallel reactions the overall rate of the process will be determined by the most rapidly proceeding reaction, while in the case of consecutive reactions, on the contrary, by the slowest reaction. In this connection, reaction (1), possibly proceeding on special active centers, is of predominant importance in the region of lower temperatures (for example, on catalysts pressed at 1000, 2500, and 10000 atm, 300°C and below, Fig. 15), and it is characterized by the fact that methanol molecules decompose into formaldehyde and hydrogen, which pass into the gas phase. The activation energy of this process for catalysts pressed at 1000, 2500, and 10000 atm is 31000–34000 cal/mol and, thus—

in this case, is numerically close to the energy of dissociation of methanol into $\mathrm{CH_2O}$ and $\mathrm{H_2}$—3100 cal.

In the region of medium and elevated temperatures, in the presence of chromium-zinc catalysts, as in the case of $\mathrm{ZnO}$ and the sulfide zinc-copper catalysts investigated by us [4, 5, 6], the consecutive reaction 2, consisting of two stages, is of predominant importance. The first stage, i.e., reaction 2a, is the slowest and, consequently, determines the overall rate of the decomposition process in the region of elevated temperatures—350°C and higher; as for the second stage, i.e., reaction 2b, it has limiting significance in the region of medium temperatures; for catalysts pressed at 1000, 2500, and 10000 atm this region lies within 300–350°C; for the other catalysts the region in which reaction (2a) proceeds predominantly lies in the wider temperature interval 275–350°C.

Some confirmation of the proposed scheme for the decomposition of methanol in the presence of the zinc-chromium catalysts investigated by us is provided by the broken-line character of the straight line $\log K = f\left(\dfrac{1}{T}\right)$ (Fig. 15), and also by the fact that, in the region of lower temperatures, the composition of the gaseous products of methanol decomposition is characterized by a high hydrogen content (~84%) and a low concentration of carbon monoxide.

In addition to the main reactions 1 and 2, side reactions occur during the decomposition of methanol; these can explain the presence in the gaseous decomposition products of such components as $\mathrm{CO_2}$, $\mathrm{CH_4}$, and other organic compounds.

The activation energy for reaction 2a, carried out in the presence of the unpressed zinc-chromium catalyst, is 19000 cal (Fig. 15 and Table 6); for the pressed catalysts $E$ was not determined by us; however, apparently, it will be close to the value given above. In the presence of pure zinc oxide, the activation energy for this stage of methanol decomposition, according to Dosa, is 22500 cal/mol; according to our studies, depending on the composition of the sulfide zinc-copper catalysts, $E$ varies from 17000 to 31100 cal/mol.

Reaction 2b is characterized by a higher activation energy; the latter, in the presence of zinc-chromium catalysts (Table 6 and Fig. 15), varies within the limits 49100–64000 cal/mol; the corresponding values for $\mathrm{ZnO}$ and sulfide zinc-copper catalysts are, respectively, 35000 and 42000–67000 cal/mol.

The observed differences in activation energies can be explained by the different composition and structure of the catalysts being compared.

As Table 6 shows, in all cases the activation energy of the pressed catalysts for the corresponding reactions is either close to, or higher than, the activation energy of the unpressed catalyst. In this connection, the increased catalytic activity of the pressed catalysts, from the formal kinetic point of view, must be due to an increase in the pre-exponential term (Const.) in the Arrhenius equation,

$$ K = \mathrm{Const.}\, e^{-\frac{E}{RT}}, $$

which, in turn, may be connected either with an increase in the reactive surface of the catalyst, or with an increase in its thermal conductivity, since in this latter case the supply of the energy necessary for the decomposition of $\mathrm{CH_3OH}$ is facilitated; it is possible that both these causes act simultaneously.

Conclusions

1. The effect of pressing (from 0 to 10000 atm) on the activity of an industrial zinc–chromium catalyst was investigated. The activity was studied by measuring the rate of decomposition of methanol vapors by the dynamic method at atmospheric pressure under conditions close to isothermal, as a function of space velocity (420–2100) and temperature (250–375°C).

2. For all the catalysts studied, the percentage decomposition of methanol vapors decreases with an increase in space velocity (or a decrease in reaction time) and increases with increasing temperature.

3. Pressing within the pressure range up to 10000 atm increases the mechanical strength and increases the activity per unit bulk volume of the catalyst. At first, with an increase in pressing pressure up to 5000 atm, the activity per unit bulk volume of the catalyst increases (with the pressure of 2500 atm constituting a certain exception), and then, with a further increase in pressure to 10000 atm, it decreases somewhat; the catalyst pressed at 5000 atm is 3–6 times more active than the unpressed catalyst.

4. The decomposition of methanol in the presence of the catalysts studied proceeds according to an apparent zero-order law; at elevated temperatures—350°C, the decomposition order tends toward first order.

The activation energies were calculated; depending on the temperature range and the catalyst pressing pressure, they amount to from 19000 to 64000 cal/mol.

1. It is assumed that the true order of decomposition of methanol vapors in the adsorption layer in the presence of the catalysts studied is monomolecular.

2. The tested process of methanol-vapor decomposition proceeds by two parallel reactions, one of which consists of two consecutive reactions:

$$ 1.\ \mathrm{CH_3OH\ ads.} = \mathrm{CH_2O\ gas} + \mathrm{H_2}, $$

$$ 2a.\ \mathrm{CH_3OH_2OH\ ads.} = \mathrm{CH_2O\ ads} + \mathrm{H_2}, $$

$$ 2b.\ \mathrm{CH_2O\ ads.} = \mathrm{CO} + \mathrm{H_2}. $$

Reaction 1 is of predominant importance in the region of lower temperatures, while reactions 2b and 2a, respectively, are important in the region of medium and elevated temperatures. The increased catalytic activity of pressed catalysts is explained by an increase in active surface and an increase in thermal conductivity.

1. The use of pressed zinc–chromium catalysts will make it possible to intensify the operation of industrial contact apparatuses, and in this connection it is necessary to undertake a study of the activity of these catalysts, starting from $\mathrm{H_2}$ and CO, at high pressures under laboratory conditions and on a semi-industrial scale.

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