GB2117366A

GB2117366A - Catalyst and method of its preparation

Info

Publication number: GB2117366A
Application number: GB08304090A
Authority: GB
Inventors: Joseph Gordon Robinson; David Ian Barnes; Angela Mary Carswell
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1982-03-12
Filing date: 1983-02-15
Publication date: 1983-10-12
Also published as: ZA831044B; JPS58166937A; GB2117366B; NL8300752A; DE3306693A1; GB8304090D0

Abstract

A novel catalyst comprises a highly porous silica having a layer of nickel bonded onto up to 50% (preferably 25%) of the surface of the silica matrix. The nickel is chemically bound into the surface by causing the surfact to react with a nickel compound. For instance nickel chloride is deposited on the matrix and caused to react therewith by treatment with a strong base. The catalyst will find use in converting an alkanol, especially methanol, to hydrogen. Thus methanol can be used to store hydrogen prior to its use as an alternative energy source.

Description

SPECIFICATION Catalyst and method of its preparation This invention relates to a catalyst for converting alkanols, especially methanol, to hydrogen and oxycarbon products. The invention also relates to a process for preparing the catalyst.

At present a large percentage of energy used in domestic heating and the internal combustion engine is derived from natural gas or petroleum oil. However, it is known that these resources are limited and therefore there has been a movement towards other energy sources.

Much interest has been shown in the use of hydrogen as an energy source. It may be used in specially adapted internal combustion engines or domestic heating appliances. As it burns to produce only water, it is a non-polluting fuel.

Hydrogen is also used to provide energy using fuel-cells.

However, the use of hydrogen as an energy source has some disadvantages associated with its storage and transport. Hydrogen as a gas very easily diffuses through most metals and plastics and therefore significant losses of it will occur if it is transported in gaseous form by pipeline. It can only be liquified at low temperatures and high pressures thus necessitating expensive storage containers.

It has been proposed to overcome these storage and transport problems by converting hydrogen to solid hydride salts from which the gas may be released in a controlled manner.

However, these hydride salts are difficult to handle, are potentially explosive and occupy a large volume per unit of hydrogen stored.

It is an aim of the present invention to provide a more effective method of storing and transporting hydrogen. The Applicants have discovered that it is possible to use liquid methanol as a store for hydrogen. This is based on the discovery of a novel catalyst which surprisingly effects the breakdown of methanol into hydrogen and carbon monoxide.

It is therefore an object of the present invention to provide a catalyst for converting methanol to hydrogen. A further object of the invention is to provide a method of preparing the catalyst, and a method of using the catalyst to produce a hydrogen.

According to the present invention a catalyst for converting methanol to hydrogen comprises a highly porous amorphous silica support having sufficient of a nickel group metal chemically bonded onto the silica support to form a monolayer on up to 50% of the total BET surface of the support.

It should be pointed out that it is known to have catalysts in which a nickel compound is deposited onto a support. In such cases the nickel compound or metal itself is only physically attached to the support. In the catalyst according to the invention, it is essential that the nickel group metal should be chemically bonded onto the surface of the silica matrix. It is in this radial fashion that the catalyst of the present invention differs from those previously known. It is believed that the silica support must have surface hydroxyl groups, preferably about four hydroxyl groups per square nanometer, to permit the reaction of a nickel group compound. It is thought that the nickel group metal is chemically bonded to the silica support to form bonds of the type nickeloxygen-silicon.Although the nickel group compound is present in sufficient amount to form a monolayer on up to 50% of the total BET surface, it may be that in places there is a thicker layer.

Preferably the metal is bonded onto about 25% of the surface of the silica matrix. Conveniently, the catalyst support has a maximum pore diameter of about 2.0 nm, although this dimension is not critical, and a suitable mean pore size is in the range 0.4 to 2.0 nm.

The metal should initially be in the +2 valency state, and it will therefore create an electrical imbalance in the matrix. Preferably the electrical neutrality of the catalyst is maintained by the concomitant introduction of protons, although other cations such as transition metal cations, lanthanide cations or ammonium ions may also be used. These cations may be used alone, in any combination, or in any combination with protons.

Preferably the metal is nickel itself, although other nickel group metals such as cobalt or iron, both in the +2 valence state, may also be used.

Amorphous silicas are known and are usually available in hydroxylated form as xerogels. In amorphous silicas, the silicon atoms are tetrahedrally co-ordinated in a matrix of oxygen atoms. In xerogel form the surface of the silica surface has a covering of hydroxyl groups, the number per unit area depending on the method of preparation. Amorphous silicas are easily prepared and are available in a wide variety of particle sizes and pore diameters. Usually most of the surface of the silica is constituted by the pore walls. These silicas are generally used as chromatography media and do not exhibit any significant catalytic activity in the conversion of methanol to hydrogen or other substances.The silica supports used in the invention are distinct from those silicas, such as porous glasses and fumed silicas, which do not have surface hydroxyl groups enabling a nickel group metal to be chemically bonded onto the silica matrix.

Preferred silica supports for use in the present invention have a surface area of about 800 m2/g.

According to a second aspect of the present invention, a method for producing a catalyst for converting methanol to hydrogen comprises treating a highly porous amorphous silica having surface hydroxyl groups with a solution of a compound of a nickel group metal, removing the solvent to leave sufficient of the compound wo form a monolayer on up to 50% of the BET surface of the silica and causing the surface of the silica to react with the compound to produce a catalyst having a layer of the metal chemically bonded onto to the silica matrix.

Any of the compound which has not reacted with the silica surface should subsequently be hydrolysed by reaction with water or an aqueous base. Thereafter, the catalyst may be heated to dehydrate the surface layer to produce complete reaction of the metal with the silica surface so that anionic sites are created on the surface of the catalyst.

Preferably the compound is a metal halide, such as nickel chloride, and is made to react with the silica surface by treatment with an aqueous base such as sodium hydroxide.

According to a third aspect of the present invention, a method of producing hydrogen from an alkanol, such as methanol, comprises passing the alkanol over a catalyst according to the first aspect of the invention, preferably at a temperature of about 4000C and preferably at a liquid hourly space velocity (LHSV) of about 1.

The hydrogen may then be used in a fuel cell, as a heating fuel or in an internal combustion engine. The other products of the reaction are oxycarbon compounds, such as carbon monoxide or aldehydes, which may be separated from the hydrogen or burned with it as a fuel. Preferably carbon monoxide formed with the hydrogen is converted to more hydrogen by reaction with steam, utilising the Shift Reaction in conventional manner.

The invention will now be described with reference to the following example which describes one particular way of putting the invention into practice. The example should not be regarded as limiting the scope of the invention, which is defined in the claims appended hereto.

Catalyst preparation Beads (100 g) of a highly porous amorphous silica gel having a mean pore diameter of 2 nm) a pore surface area of 800 m2/g, a pore volume of 0.4 cm3/g and a particule size of 125 microns were placed in a flask and the pressure therein was reduced to about 1 mm Hg. Sufficient aqueous nickel chloride solution (0.38 g/cm3) was added to cover the beads. The partial vacuum ensured that the solution completely penetrated the pores of the gel. After standing overnight, the gel was collected by filtration and dried at 500C under reduced pressure (1 mm Hg). When cool, the gel was covered with aqueous sodium hydroxide solution (0.24 g/cm3) and left to stand for 1 8 hours. Thereafter the gel was waterwashed until the washings were neutral. The washed gel was dried at 1 000C for 4 hours.

The calcined product comprised silica gel having nickel atoms bonded onto about 25% of its surface area, the electrical neutrality of the gel being maintained by sodium ions.

The calcined product was covered with a 10% aqueous solution of ammonium chloride and the pressure was reduced to facilitate penetration of the solution into the pores. The temperature was raised to 900C and after 1 hour the gel was filtered and water-washed. This process was repeated until no more sodium was removed (as indicated by flame testing). The gel was waterwashed again, dried at 1 200C for 4 hours and calcined at 5000C for 4 hours. This process produced a catalyst in which electrical neutrality was maintained by protons derived from ammonium ions with concomitant evolution of ammonia gas.

A second catalyst was prepared in similar manner, but using a nickel c#loride concentration of 0.76 g/m3. This gives a catalyst having nickel atoms reacted onto about 50% of the surface area of the silica support.

Catalyst evaluation The catalyst beads were placed in an electricaliy heated stainless steel tube and held at a temperature of 4000C. Methanol was fed from a storage reservoir through a container holding glass beads at 3750C wherein the methanol was heated to 3750C. The methanol vapour was passed over the catalyst at a LHSV of about 1.0 h-1. The products emerging from the catalyst bed were collected in gas traps and analysed by standard chromatographic procedures.

It was found that the catalyst with 25% nickel cover converted almost quantitatively (-95%) methanol to hydrogen and carbon monoxide. The catalyst maintained its activity in tests extending up to 12 hours. The efficiency of conversion was reduced as the temperature of the catalyst bed was reduced.

For the catalyst with 50% nickel cover, the degree of conversion was only about 5%.

It can thus be seen that the catalyst according to the present invention very efficiently converts methanol to hydrogen and carbon monoxide. This is most surprising as generally nickel based catalysts, for instance nickel impregnated zeolites, are used to convert methanol or synthesis gas to hydrocarbons, such as methane and ethane. It was therefore unexpected to find that the catalyst according to the invention was able to convert methanol to hydrogen and carbon monoxide. Pure hydrogen may be separated from the mixture a variety of well known techniques. However, it is preferred that the carbon monoxide is reacted with steam in a normal Shift Reaction to prnduce hydrogen and carbon dioxide. The carbon dioxide and excess steam are easily removed from the hydrogen.

The present invention therefore provides a new and useful way of converting a hydrogen store (methanol) into hydrogen gas in a safe and efficient manner.

Claims

1. A catalyst for converting methanol to hydrogen comprising a highly porous amorphous silica support having sufficient of a nickel group metal chemically bonded onto the silica support to form a monolayer on up to 50% of the total BET surface of the support.

2. A catalyst according to claim 1, wherein the metal covers about 25% of the surface.

3. A catalyst according to either one of claims 1 or 2, wherein the metal is nickel itself.

4. A catalyst according to any one of the preceding claims, wherein the support has a surface area of about 800 m2/g.

5. A catalyst according to any one of the preceding claims, wherein the support has a mean pore size in the range 0.4 to 2.0 nm.

6. A catalyst according to any one of the preceding claims, wherein the support is a silica rogel.

7. A catalyst according to any one of the preceding claims, wherein the electrical neutrality of the catalyst surface is maintained substantially only by protons.

8. A catalyst substantially as hereinbefore described, with reference to the example.

9. A method for producing a catalyst according to claim 1, comprising treating a highly porous amorphous silica support having surface hydroxyl groups with a solution of a compound of a nickel group metal, removing the solvent to leave sufficient of the compound to form a monolayer or up to 50% of the BET surface of the silica, and causing the surface of the silica to react with the compound to produce a catalyst having a layer of the metal chemically bonded onto the silica support.

1 0. A method according to claim 9, and including the step of hydrolysing any unreacted amount of the compound.

11. A method according to either one of claims 9 or 10, wherein the compound is a nickel halide.

1 2. A method according to claim 11, wherein the compound is caused to react with the surface of the silica support by treatment with an aqueous base.

13. A method according to any one of claims 9 to 12, wherein the silica support has a surface area of about 800 m2/g.

14. A method according to any one of claims 9 to 13, wherein the silica support has a mean pore size in the range 0.4 to 2.0 nm.

15. A method according to any one of claims 9 to 14, wherein the support is a silica xerogel.

16. A method according to any one of claims 9 to 1 5, comprising also the step of introducing protons as substantially the only electrical charge balancing species on the catalyst surface.

1 7. A method for producing a catalyst for converting methanol to hydrogen, substantially as hereinbefore described with reference to the example.

1 8. A catalyst when made according to the method of any one of claims 9 to 17.

19. A method of producing hydrogen from an alkanol, comprising passing the alkanol over a catalyst according to any one of claims 1 to 8 and 18.

20. A method according to claim 19, wherein the alkanol is methanol.

21. A method according to claim 19 or 20, wherein the reaction temperature is about 400 C.

22. A method according to any one of claims 19, 20 and 21, wherein the alkanol is passed at a LHSV of about 1 h-'.

23. A method according to claim 19, and including the step of treating the product from the catalyst by a shift reaction to increase the hydrogen content of the product.

24. A method of producing hydrogen from methanol, substantially as hereinbefore described with reference to the example.