US2315518A - Method of activating catalytic surfaces - Google Patents

Description

Filed 0st. 3, 1939 Q1 ACTIVATING CATALYTIC SURFACES Patented Apr. 6, 1943 OFFICE METHOD OF ACTIVATING CATALYTIC SURFACES Marion H. Gwynn, Mountain Lakes, N. J.

Application October 3, 1939, Serial No. 297,651

4 Claims.

This application is continuation-impart of my copending applications Serial No. 130,478 filed March 8, 1937, now Patent Number 2,174,510, granted October 3, 1939, and Serial No. 240,447 filed November 12, 1938. This invention relates to catalysts and to the preparation and reactivation of active metallic type catalytic surfaces, particularly those adherent or fixed to the underlying metal. These treated surfaces are especially adapted for use in hydrofining, i. e. hydrogenating and/or refining oils and other organic or carbonaceous compounds. The surface layers may also be used as reagents, as for example in the formation of metallic sulphides; or as adsorption or purifying agents, as in the treatment of vegetable or, animal glycerides before steam deodorization, or as when doctor sweetening light petroleum or like distillates, or as tower packing or otherwise.

The essential activating step of my invention is an anodic peroxidation in an aqueous alkaline electrolytic bath, preferably containing the hydroxidc of a heavier alkaline earth metal, to pro- "aduce a surface which is catalytic with respect to sulphur sensitive hydrofining without further chemical treatment. These hydroxide electrolytes may be used in extraordinarily low concen-- trations. Anodic oxidation on metals using salts as electrolytes together with a subsequent reduction in hydrogen before use has been proposed for the production of active precipitated metallic catalysts. However either powder or fixed catalyst so prepared fails to maintain its activity substantially uniform during hydrofining. During electrolysis, salt electrolytes readily change in composition, and also allow sulphate ion to accumulate in the electrolyte and hence are impractical for the removal of sulphur from fixed metal surfaces without removing catalytic metal itself. Moreover I find that salts are generally deleterious in the electrolyte, increasing polarization and exerting a depressive effect On the adherence and activity of the catalyst anodically oxidized in their presence.

I also find that oxidizing treatments prior to my anodic per-oxidation improve the activation, particularly when activating cobalt or nickel surfaces. The preferred form of my invention comprises activating or peroxidizing a metallic surface previously subjected to an oxidizing treatmenl, in an anodic peroxidation bath as described. For example I may prepare highly active black fixed catalytic surfaces or surface layers by preliminarily treating a metal such as cobalt or nickel in a foraminate state to form a hydrated and/or a moderately catalytic surface layer. This pre-treatment may be effected by anodic oxidationand deposition in an alkaline bath or by anodic activation in an acid bath, particularly on cobalt, or by other chemical means.

The surface comprising this hydrated or moderately catalytic layer is then rendered further catalytic and is peroxidized at the anode in an electrolytic bath which contains a substantially saturated and unheated aqueous solution of a hydroxide of a metal selected from the group containing calcium, strontium, and barium. The catalyst produced in this way without further chemical treatment is highly catalytic and ready for use in sulphur sensitive hydrofining operations, and may maintain its activity substantially uniform during hydrofining until spent. This catalyst is not a precipitate, but is substantially integral with metal beneath the catalytic layer. Instead of starting with a new metal surface I may start with catalyst which has been used, for instance'a sulphur bearing surface layer may be anodically desulphurized and activated without loss of metal from the surface, since the sulphur is reacted with the electrolyte and precipitated out of solution as an insoluble sulphate.

Salts, whether or not forming soluble compounds with the catalytic metal, are tolerated to a limited extent and may be present in my alkaline electrolytic bath, provided that hydroxyl is the predominant ion in the anolyte. Thus when a fixed and sulphided surface of a metal is anodically activated in an alkaline solution other than strontium hydroxide or barium hydroxide, sulphate ion may accumulate in solution and dissolve catalytic metal when the sulphate and other salt anions are predominant over hydroxyl ion in the anolyte. If anions other than hydroxyl are present in my alkaline electrolytic bath, they should not predominate in the anolyte. For in stance, when a fixed and sulphided surface of a metal is anodically activated in an aqueous solution of calcium hydroxide, the solution is preferably changed before the sulphate ion exceeds the hydroxyl ion in concentration and activity in the anolyte, on account of the solubility of calcium sulphate.

I mayalso use as anodic peroxidation electrolytes soluble alkaline hydroxide solutions similarly low in thermodynamic activity to the solutions of the hydroxide of calcium, strontium, barium. For example I may also use a cool one normal solution of lithium hydroxide. Generally, however, the alkali metal hydroxides appear incapable of anodic peroxidation. It is my belief that this is due to their high thermodynamic activity coefficients.

I may employ my alkaline electrolytic activation substantially without other chemical treatment, particularly for the activation of the lesser catalytic and hydrogenating metals such as lead or tin or copper or silver, which however are catalytic for desulphurization rather than hydrogenation.

My invention is not limited to lead or tin or cobalt or nickel or copper or silver, which as a group are remarkably desulphurizing and reacti-- vatable, but may be applied to other metals, including alloys comprising one of the above elements or alloys similar to cobalt or nickel, ferromagnetically similar, for example. The catalytic surfaces resulting from my anodic peroxidation, particularly those black in color, appear to possess a crystal lattice parameter substantially longer than that of the normal oxide. It is withimt/he contemplation of the invention to activate metal of face center cubic crystal lattice, neither extremely electropositive nor electronegative, especially those which in the activated state are catalytic for the following vapor phase triple decomposition between 200 C. and 300 C. or like reaction:

R is olefinic and M is a metallic element or mixture and x is specific within limits for each metal, varying for example from about 1 for lead and 1.2 to 1.5 for the more active metals such as cobalt and nickel, to between 1.6 and 2 for copper and silver.

Peroxidation appears naturally adapted to the reactivation of desulphurizing surfaces, since oxygen and sulphur are elements of the same -periodic family and since Oz has the same molecular weight as S1. Sulphides of these peroxidiz able catalytic metals are black, and the surfaces activated by .my anodic peroxidation are also preferably black in color. Of the several peroxidizable metals, three are'particularly related and active and useful when activated as. described herein. Thesethree are nickel and the two elements of adjacent atomic number, cobalt and copper.

Catalytic surfaces prepared and deactivated with use as described in my copending application, Serial No. 130,478, may be reactivated by a. process comprising my anodic peroxidation. Likewise the catalysts herein disclosed may be used in the desulphurization of organic compounds as set forth in my U. S. Patent 2,073,578 or in my corpending application, Serial No. 130,478., new U. S. Patent 2,174,510. The values of a: in Mr above are related to the original activity of the catalyst and to the manner in which I may carry out that desulphurization. Desulphurization of organic compounds by these catalysts is preferably accompanied by hydrogenation, particularly replacing the sulphur with hydrogen. The organic sulphur compounds are preferably in hydrocarbon solution as with crude motor fuels. MIS is readily reconverted electrolytically to MrO2-2H2O or like compound by my invention as described herein.

In the drawing:

Fig. 1 represents a perspective view of an assembly of screen discs;

Fig. 2 represents a diagrammatic view showing 75 the relative positions of a disc or other assembly and a cathode disc;

Fig. 3 represents a perspective view of another form of assembly; and

Fig. 4 represents a diagrammatic showing of apparatus for the continuous anodic activating assemblies and for replenishing the electrolyte.

I will now give some examples ofhow my invention is to be practiced, but I am not to be limited thereto, as they may be modified in many particulars without departing from the spirit of the invention. Before chemical activation, but not reactivation, each assembly may be physically treated to increase the initial foraminate charactor of the assembly, as described near the end of specification. The resulting activated surfaces have general as well as specific usage.

Example I The assembly 10 is composed of several cobalt or cobalt coated screens designated by the reference numeral l2. These screens are 12.7 cm. in diameter fastened together so that their centers lie along a straight line to form a disc assembly as shown in Fig. 1. The diameter of each Wife of the screen is about 0.04 and the adjacent parallel wires are 0.24 cm. apart on centers. This disc assembly I!) is placed in a bath with its principal plane parallel to a flat circular nickel sheet cathode 14 also 12.7 cm. in diameter as shown in Fig. 2. The bath (not shown) contains an electrolyte composed of commercial water glass at about 35 C. and a current density of about 8 milliamperes per sq. cm. and 4.6 volts are applied for sufficient time to form on the surface of the screens a deep blue coating containing hydrated silicate which is a dehydration promoter. This is a preliminary oxidizing treatment.

The screens are withdrawn from the water glass bath and the excess silicate and deposited hydrated silica may be removed with an aqueous solution of half normal sodium hydroxide at, about 60 C., at the same time converting part of the cobalt silicate to cobalt hydroxide. The screen surfaces are then given a further anodir: activation in another aqueous bath containing calcium hydroxide saturated at 5 C. Sufficient voltage is impressed on the calcium hydroxide bath to maintain a current density of about 5 milliamperes per sq. cm., and this is continued for about one quarter hour or until the current efiiciency substantially diminishes. The screens are then withdrawn and washed, being catalytic without further treatment. Other alkaline electrolytes depositing a dehydration promoter in the surface layer may be substituted for the water glass, particularly those which are concentrated and colloidal and which gel on the slight addition of acid.

Example II A new cobalt assembly of the same internal and external shape and size as described in Example I is highly peroxidized in the following manner. The assembly is connected as the anode and pretreated in an electrolyte composed of 4 normal aqueous hydrofluoric acid at 5 C. The cathode and its placement are also as described in Example I. The current density and voltage are adjusted to form a deep adherent black layer on the cobalt assembly. About 4 volts are first applied, or a voltage sufiicient to produce a current density on the order of 30 milliamperes per sq. cm., and when after a few minutes the current density or current efficiency diminishes, the potential may be increased continuously or at intervals t about volts or higher. When the current efficiency substantially decreases or when a deep black surface layer is formed, the hydrofluoric acid is withdrawn from the bath, and the treated cobalt assembly is drained and washed. A new electrolytic bath is then run in composed of about 0.04 normal solution of calcium hydroxide at 5 C., which is a nearly saturated solution. A current density of about 3 or 4 milliamperes per sq. cm. and a voltage of 4.6 is applied for several minutes or until the fluorine is displaced from the surface.

All steps in my invention may be electrolytic, for instance in Example II washing when used may be facilitated by electrodialysis. 1

Other metals may be substituted for cobalt in Example II, for instance an alloy of cobalt containing nickel or palladium. Strontium or barium hydroxide or milk of lime may be substituted for the calcium hydroxide. Other strong acid electrolytes may be substituted for the hydrofluoric acid, preferably decomposable and in a dilute solution. Such acids with or without impressed electrical potential may be used to treat these and other surfaces prior to my anodic peroxidation.

Hydration of the surface layer prior to my anodic peroxidation may be obtained as in the previous examples, or during reactivation with steam or hypohalites, or by other methods or combinations of methods.

Example III A new copper assembly composed of pure copper turnings whose superficial area is about 1,000 sq. cm. is packed in a rectangular boxlike container cm. high and 10 cm. wide, composed of coarse open copper screening. The assembly is placed in a bath with its 10 cm. by 10 cm. faces parallel and opposed to a square sheet nickel cathode also 10 cm. by 10 cm. Thus the facial area is 100 sq. cm., identical to the 12.7 multiplied by 1%; pi of the circular discs of Fig. 1. The assembly is'heated for several hours in air at the lowest temperature required to form a dark oxide coating on the entire surface, for instance near 300 C. The oxidized turnings and screen are then connected as the anode in an aqueous electrolytic bath containing about 0.5 normal barium hydroxide at about 30 C. Sufficient voltage is applied to maintain a current density of 10 to 20 milliamperes per sq. cm., and when the electrolytic peroxidation is initiated the cur rent density is lowered somewhat below 10 milliamperes per sq. cm., and the electrolysis continued until the current efficiency substantially diminishes. The catalyst is then withdrawn, drained and washed. Should the air oxidized turnings only respond to the anodic peroxidation to a low degree as noted by a relatively low early current efficiency, they may be washed and reactivated as follows: Reduce in hydrogen at about 200 0., cool in steam, and then repeat the air oxidation given above, and anodically treat as given before.

Pure silver may also be treated in this manner with or without preliminary air oxidations.

Example IV The assembly I6 is composed of several new nickel or nickel coated screens of the same area, wire and weave as the screens in Example I. The nickel or nickel coated screens l8 are square instead of circular however, each 10 cm. x 10 cm., and fastened together on at least one edge 20 as in a book. The external dimensions are those of the assembly in Example III. The surfaces of the screens are pretreated several hours with the vapors of concentrated nitric acid at 40 C. or 50 C. to pit and oxidize the nickel surface to form a nitrate of nickel, and then without washing, the mass is dried and gently heated in a current of air above about 200 C. and/or at near the lowest temperature required to evolve fumes and decompose a substantial portion of the resulting nickel nitrate and darken the mass, for instance at about 300 C. This assembly, now moderately catalytic, is placed parallel to a square nickel sheet cathode as given in Example III, in an electrolyte composed of a one-thirtieth normal aqueous solution of calcium hydroxide at about 15 C., and a voltage of about 4.6 volts applied until a current of about 2 amperes passes, i. e. a current density of 20 milliamperes per sq. cm. As soon as blackening begins the amperage is reduced to about 0.4, i. e. a current density of 4 milliamperes per sq. cm., and the electrolysis continued for at least an hour or until no further darkening is noted or' until the evolution of oxygen approaches one-half the volume of the hydrogen. After electrolysis, the solution is withdrawn from the bath and the screen assembly carefully washed with water, being catalytic without further treatment.

Other surfaces may be treated with nitric acid prior to my 'anodic peroxidation, for instance a new cobalt surface, or the new copper surface described in Example III.

Example V The assembly is the peroxidized nickel assembly such as described in Example IV, then nearly used to capacity in a desulphurizing operation such as represented by the chemical equation above given, and subsequently steamed at least sufficiently to remove the hydrocarbons. This spent assembly is then made the anode in an electrolyte composed of an aqueous substantially saturated solution of strontium hydroxide at room temperature. A current density of 10 milliamperes per sq. cm., or as much higher current density as needed to initiate reactivation is applied for a few minutes, and then the current density is gradually reduced to about 4 or 5 milliamperes per sq. cm. The electrolysis, is continued until most of the sulphur is removed or until tests on the electrolyte indicate the cessation of strontium sulphate formation; Without further chemical treatment, the catalyst may then be used again, preferably for the same use as before.

Lead tolerates higher sulphate ion concentrations in the electrolyte than the other catalytic metals. Thus I may operate the process as described in Example V, but starting with a cold saturated calcium hydroxide electrolyte, and with lead instead of nickel as the metallic component in the surface layer.

Nickel or copper or like surfaces sulphided by adsorption of heated organic sulphur vapors and/or liquids without added hydrogen at relatively low non-pyrolytic temperatures, may be treated by my invention, as in Example V. The electrolyte may be replenished by circulation over solid strontium hydroxide or by the addition of a hot saturated aqueous solution of strontium hydroxide, first however separating out any precipitated strontium sulphate as by settling or centrifuging or filtration.

In Fig. 4 I have shown a diagram of an arrangement for continuous anodic peroxidation,

recirculating the electrolyte in contact with a hydroxide such as the strontium hydroxide as mentioned above. The reference number 22 designates the electrolytic tank slightly tilted toward orifice 24 and containing the aqueous alkaline earth metal hydroxide electrolyte. Above the electrolytic tank is an electrode conveyor 23 for continuously moving the electrodes from right to left during anodic peroxidation. The catalyst assemblies 28 are connected by metal anode connectors 21 to the conveyors anode bar 29. Between each assembly 28 and parallel thereto are sheet nickel cathodes 30, connected by metal cathode connectors 3| to conveyor's cathode bar 33. The electrodes enter the tank or bath in relatively spent electrolyte 25, and emerge from a relatively fresh electrolyte 26. Thus the reactivation is countercurrent with respect to spending of the electrolyte. The relatively spent electrolyte 25 passes through pipe 32 to a settling tank 35, containing a false bottom 36 which may be lifted out by a device 38 together with impure alkaline earth metal sulphate and other solids which have settled out. The settling tank has a loose cover 40. The overflow from the settling tank passes through pipe 42 to a centrifuge 44 and the clarified alkaline earth metal hydroxide passes through pipe 48 to covered tank 48 provided with vent 50. The centrifuge is provided with means to remove solid material. processed to convert precipitated alkaline earth sulphates to hydroxide electrolyte in apparatus not shown. A pipe 52 leads from the bottom of tank 48 to pump 54 and by means of the pump the liquid is piped to hydroxide replenishing chamber 58 containing a hydroxide such as strontium hydroxide in a heated aqueous solution or as the octahydrate. A substantially saturated hydroxide solution 26 may pass from chamber 58 through pipe 60 and orifices 62 back to the electrolytic tank 22.

Thus a surface layer comprising nickel sulphide and/or sulphate is treated by means of double decomposition between the surface layer and the electrolyte, preferably adding a hydroxide of either calcium, strontium or barium to the bath during the electrolysis. The resulting precipitated alkaline earth metal sulphate may be collected and reconverted to hydroxide, as with an alkali of sodium. For instance strontium sulphate may be autociaved with sodium carbonate solution forming sodium sulphate, and the resulting strontium carbonate converted to strontium hydroxide in a current of gas comprising superheated steam. If barium compounds are used instead of those of strontium, the barium carbonate generally requires coke and air for its conversion to alkali. Strontium sulphate or barium sulphate may be otherwise converted to their hydroxides, for instance they may give up their sulphate to a calcium compound forming calcium sulphate.

Or a surface layer substantially a metal sulphide may be desulphided at least in part prior to anodic activation, e. g. nickel sulphide or cobait sulphide may be strongly heated with an oxygen gas and/or steam to convert most of the sulphides to oxides, then these oxide films may be further treated until sufficiently hydrated to respond to anodic peroxidation.

The surface layer prepared for my anodic peroxidation may consist of a characteristically colored salt, and such salts are generally hydrated.

This and the solids from 36 may be If such a salt resists anodic peroxidation, its resistance may be decreased by further treating prior to anodic peroxidation, for instance treating with a strong alkali solution as given in Example I to change at least a portion of the salt to the hydroxide. I may treat other surfaces, particularly surfaces consisting of a compound of the catalytic metal other than the sulphide, with heated and/or strong alkalies preliminary to anodic peroxidation. The concentration of said strong alkali is preferably high, but not extreme. If the preliminary surface layers of the more active metals are not well hydrated, the surface layer should be relatively deep, especially on metals like cobalt. A relatively shallow layer of adherent nickel hydroxide, or a somewhat thicker layer of cobalt hydroxide suflices to initiate deeper oxidation of the catalytic surfaces with my anodic peroxidation. The surfaces more activated by my invention require the more catalytic preliminary surface layer. For instance, the metals which are both the more catalytic and form the higher oxides require the more hydrated and/or deeper preliminary layer. The less oxidizable and adherent the layer, the more hydrated and/or deeper is the required preliminary layer.

The peroxidation of the surface layers appears to be quite autocatalytic so long as the chemical potential required for the peroxidation is less than about 1 volt. Hence those agencies which initiate peroxidation are useful, and result in better activation and substantial savings of current and time. For instance, the more activatable compounds in the surface or formed on the surfaces by proper pretreatments, during their peroxidation initiate the peroxidation of the more difiicultly activatable compounds or of the underlying metal itself, Non-cotalytic surface layers containing only a slight amount of hydrated compounds preferably oxidizable respond to anodic peroxidation. A hydrofining catalyst prepared by my invention and substantially but not entirely spent constitutes such a surface=lay er. Successive reactivations are generally; accompanied by increases of depth of a surface layer and receptivity to the activating treatment, especially when hydrogenating at low temperatures. My invention is not to be restricted to the theories expressed herein.

The catalyst may be removed from the hydroflning chamber or the tower for reactivation or may be reactivated in place when properly insulated. The cathodes may be sheet Monel metad or nickel and treated to lower the overvoltage.

A diaphragm between the electrodes may be provided. The removal of oxygen from the anode surfaces, especially during the latter stages of peroxidation, may be facilitated as by imparting motion to the anode or anolyte.

I prefer that the voltage of the peroxidation baths comprising the hydroxides of calcium or strontium or barium be between 4V2 and 6 volts, and that the temperature be maintained below about 50 C. The current density of these and other alkaline electrolytes may be started at a current density of 20 milliamperes per sq. cm. of facial area and then decreased, for instance rapidly at first, slowly at the end. I prefer that these current densities be maintained above 1 milliampere per sq. cm. of facial area, and the average current density below about 10 milliamperes per sq. cm. of facial area.

The current density is preferably closely adjusted near the lowest current density at which ,tion of the nickel anode.

relatively high current efficiency canbe obtained, especially during the earlier or intermediate portions of the anodic activation in the low activity coefficient electrolytes. However the current density may be sufficiently high during the initial stages of the electrolysis to initiate oxidation without loss of surface. I prefer that the product of the current density and current efficiency be decreased during the activation at the anode, particularly at the extreme portions of the activation.

' The current may be continued until the current efficiency at constant current density markedly decreases, or until practically no further peroxidation occurs, or until a layer of activated oxide covers the surfaces to a depth of 10 to 10 catalytic metal atoms, for example an average depth of 10 catalytic metal atoms, or until the surface is highly catalytic, or until sufficiently catalytic for active hydrofining without further chemical treatment. The time of electrolysis is proportional to the ratio of the superficial area and the facial area, and is also proportional to the depth or the activated surface layer.

In the foregoing examples, the total superficial area of each assembly, internal and external, is about 100 to 1,000 sq. cm., the facial area of each assembly is 100 sq. cm., and the ratio thereof termed th surface facial ratio, is about 1 to 10. The screens may be extended in length and/or breadth without changing the ratio. If an assembly is composed of wire for instance, the superficial area is the area of a very long solid cylinder whose diameter is that of wire.

I prefer that the size of the cataly t. assemblies be so limited that the surface facial ratio is ordinarily less than 50. When coating an assembly with an adherent and rough coating as by electroplating, I prefer that the assembly being electro- Dlated be so limited that the surface facial ratio is less than about 20. The electroplate is preferably heavy, particularly on the faces'nearest the electroplating anode, and may be applied by a method known to the art, particularly under conditions of good throwing power. The current density may be increased as the electrodeposit thickens and particularly the electrodeposition may take place at near the highest cathodic current density at which an adherent porous electroplate is'obtained. An example of a nickel platin bath is a strong iron free aqueous solution of nickel sulphate together with sufficient minor quantities of boric acid and nickel chloride or ammonium chloride to maintain uniform dissolu- The nickel is preferably plated on a copper or copper coated iron assembly.

In the preparation of fixed catalyst on metal, especially when prepared on wire or like superflcial forms, I prefer that the metal prior to chemical activation be machined so as to produce burrs or grooves or worked as with heat, and/or alloying to produce fine longitudinal cracks. Similarly sheet metal or stampings are preferably perforated or knurled before assembling. Fixed catalyst, such as a foraminated base metal or rough inert solid, and whose surfaces comprise nickel or cobalt or silver or like catalytic metal,

or ores or catalytic surfaces accessible to electrolysis and prepared by the various methods of the art, may be activated or reactivated according to my invention.

The methods and constructions described herein may be used in conjunction with other treatments or otherwise used. For instance the assemblies before or after the chemical treatment given herein may be finally activated as described in my copending application Serial No. 117,515 filed December 24, 1936, now U. S. Patent Number 2,191,- 464. Or the methods described herein may be a used in conjunction with'those of my copending application Serial No. 240,007 filed November 8, 1938, now U. S. Patent Number 2,270,874, as indicated therein. Or anodically peroxidized surfaces may be contacted with an aqueous solution comprising chromic acid or ammonium molybdate or nickel nitrate. Or anodic peroxidation may be followed by reduction in hydrogen. particularly when the reduced catalyst. is subsequently used for the hydrogenation of unsaturated natural glycerides. After hydrogenating and/or purifying fatty or like compounds. these compounds or impurities may be extracted, as by refluxing with volatile hydrocarbons. Or more polar s01- vents such as dichlorethylene or acetone may be used, particularly for a final extraction or when using the catalyst as a purifying agent.

What I claim is:

1. A process for preparing a metallic catalytic surface whose catalytic element is selected from the class consisting of cobalt, nickel and copper, comprising activating the surface at the anode in an electrolytic bath consisting substantially of an aqueous solution of a hydroxide of a metal selected from the class which consists of lithium, calcium, strontium, and barium, thereby forming on the surface a hydrated higher oxide of said catalytic element.

2. A process as described in claim 1, in which the electrolyte temperature and thermodynamic activity coefficient are relatively low.

3. A process for preparing a metallic catalytic surface whose catalytic element is selected from the class consisting of cobalt, nickel, and copper, comprising subjecting the surface to an oxidizing treatment and subsequently further activatin said surface at the anode in an electrolytic bath consisting substantially of an aqueous solution of a hydroxide selected from the class which consists of lithium, calcium, strontium, and barium, thereby forming on the surface a hydrated higher oxide of said catalytic element.

4. In the art of reactivating a metallic catalytic surface whose catalytic element is selected from the class consisting of cobalt, nickel, and copper, and which is substantially deactivated in the hydroiining of hydrocarbon distillates containing impurities of organic sulphur compounds, the process comprising reactivating said surface at the anode in an electrolytic bath consisting substantially of an aqueous solution of a hydroxide of a metal selected from the class which consists of lithium, calcium, strontium, and barium, thereby forming on the surface a hydrated higher oxide of the catalytic element.

MARION H. GWYNN.

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