RO107842B1 - Hydrophobic platinum catalysts preparation process - Google Patents

Abstract

The invention relates to a process of preparation of platinum catalysts, hydrophobic, active and stable in the isotope separation process hydrogen, by isotope exchange of water - hydrogen and in the catalytic recombination process a hydrogen and oxygen. The process uses hydrophobic supports with a high specific surface area 700 ... 900 m2 / g of styrene type of divinyl benzene and hydrophilic supports with a particular surface area high 1200 ... 1700 m2 / g, coal type active or superactivated, impregnating with acid hexa-chloroplatinate dissolved in a solution of two components, a component in which the acid is readily soluble, acetone and a component in which hexachloroplatinic acid is not soluble, benzene, in a volume of acetone: 1: 5 benzene, preferably 1: 3, after which the impregnated support is dried perform at a temperature below 65 ° C, preferably 55 ... 60 ° C and under vacuum at a pressure of 10-1 ... 10 ° C at, to constant mass.

Description

The invention relates to a process for the preparation of platinum catalysts, hydrophobic, used in the processes of hydrogen exchange and catalytic recombination of hydrogen with oxygen.

The object of the invention is the preparation of platinum catalysts, hydrophobic, with high activity and long stability, under the conditions of direct contact with liquid water, used as a reactant or as a cooling agent.

In the process of hydrogen isotope separation, by the chemical exchange of hydrogen water according to the reactions:

HDO _(V) + H ₂ H ₂ O _(V) + HD _{(£ 1} (1)

HT0 _(V) + H _{2 (&} > H ₂ O _(V) + HT _U) and in the process of catalytic hydrogen-oxygen recombination, catalysts of the type of transition metals (Ni, Pt, Pd) are known on the substrate, but they work. only in dry environment requiring reaction temperatures higher than saturation for process (1) or temperatures of 300 ... 400 ° C, in the process of recombination, which accelerates the thermal degradation of the catalysts.

Also known are hydrophobicized catalysts of the above type, which gives them stability in direct contact with liquid water, but the conditions for intermediate stages of preparation, as well as the use of hydrophobic supports (polytetrafluoroethylene, polystyrene, polyethylene, stirendivinyl benzene) or hydrophilic substrates, subsequently hydrophobicized (alumina, silica or coal) medium specific surface supports result in average sizes of the active metal crystals, respectively average catalytic activity.

The process for the preparation of platinum catalysts, hydrophobic, of the type: Platinum / Cbb / Teflon (Pt / C / PTFE): platinum / styrene vinyl benzene / polystyrene (Pt / SDB / PS) and platinum / styreneivinyl Benzene / Teflon (Pt / SDB / PTFE), according to the invention eliminates the disadvantages of known processes, by using hydrophobic media with a large specific surface area of 700 ... 900 m ² / g, of the divine styrene type benzene and hydrophilic media with a specific surface area high 1200 ... 1700 m ² / g of the type of activated or super-activated charcoal, which is impregnated with hexachloroplatinic acid dissolved in a solution composed of two components, a component in which the acid is slightly soluble: acetone and a component in which the acid hexachloroplatinic is not soluble, benzene, in a volume ratio acetone: benzene of 1: 5 preferably 1: 3, after which the drying of the impregnated support is carried out at a temperature below 65 ° C, preferably 55 ... 60 ° C and under vid the o pr 10 ' ¹ ... IO' ² session, up to constant mass.

The process of preparing hydrophobic platinum catalysts according to the invention has the following advantages:

- uses hydrophobic supports (SDBs), with a specific surface area of 700 ... 900 m ² / g or super-activated hydrophilic coals, with specific surfaces, between 1200 ... 1700 m ² / g;

- uses, as a precursor of the catalytic active metal, hexachloroplatinic acid, dissolved in a solution consisting of a component in which the hexachloroplatinic acid is readily soluble, for example, acetone and a component in which the hexachloroplatinic acid is hardly soluble, for example, benzene , in volume ratio of 1: 5 preferably 1: 3.

The use of acetone - benzene solution greatly enhances the uniform distribution of hexachloroplatinic acid over the entire inner surface of the pores, because, due to the higher volatility of acetone and the insolubility of benzene acid, it is avoided to redissolve the acid in solution, at its liquid-solid interface.

- the drying of the impregnated substrate is carried out, to avoid thermal decomposition of the acid, at a temperature below 65 ° C, preferably 55 ... 60 ° C and at a pressure of 10 ' ¹ ... IO' ² torr, based on water, in a rotary evaporator under vacuum;

- realizes a platinum / styrene catalyst divinens bensen / polystyrene (Pt / SDP / PS) agglomerated in the form of spheres of 3 ... 5 mm, by the droplet method using a benzene solution of polystyrene, of concentration 1 ... 10% , preferably 5% thus preserving the porosity and hydrophobicity of the impregnated support.

The catalysts thus prepared are characterized by an advanced porosity, which ensures the rapid access of the reactants to the active centers, catalyticly, a uniform dispersion and a platinum particle size below 15 Â, which leads to a high activity, as well as a high activity. prolonged stability, due to the hydrophobic character of the support or the combination of the hydrophobic character of the support with that of the binder (Teflon, polystyrene).

The following are examples of embodiments of the invention. 10

Example 1. Preparation of the Pt / C / PTFE catalyst The active or superactivated, crushed coal support is located by choosing the fraction with dimensions between

2 ... 3 mm, it is then subjected to vacuum, for the removal of gases and vapors adsorbed in a rotary evaporator, under vacuum at 10 ' ¹ ... IO' ² torr and ambient temperature, for 1 ... 2 h.

A determined amount of hexachioroplatinic acid is dissolved, at room temperature, in acetone p.a. and after complete dissolution, a volume of benzene in a volume ratio of 1 ... 3 is added to the solution.

The concentration of the hexachioroplatinic acid solution will be chosen, depending on the desired concentration in the final catalyst and on its composition.

A batch of 100 g of vacuum support whose absorption capacity has been previously determined is impregnated, at room temperature 30, with 120 ml of hexachloroplatinic acid solution in acetone and benzene, for 5 to 6 hours, after which they are removed. , by filtration, the excess impregnation solution.

The impregnated support is dried in a rotary evaporator under vacuum at 10 ' ¹ ... IO' ² towers on the water bath at a temperature of 60 ° C, until constant mass.

In order to obtain the catalytic active metal particles, the substrate thus impregnated and dried is subjected to reduction in an oven at 100 ... 200 ° C, preferably 150 ° C, in a hydrogen atmosphere, in a hydrogen ratio: support volume of 200: 1.

The coal thus platinized is softened and lies below 0.08 mm in size and is mixed homogeneously with teflon powder in a mass ratio of 1: 25.

The resulting mixture is subjected to molding, in the form of Rasching rings or cylinders at a pressure of 2 ... 3 at and then sintered in an oven, at 360 ° C, for 30 minutes.

Example 2. Preparation of the Pt / SDB / PS catalyst The platinum-stained benzene styrene support, as in example 1, is subjected to agglomeration, in the form of spheres of 3 ... 5 mm in diameter, by the droplet method, using a benzene solution of polystyrene. , of 5% concentration, followed by drying, in an oven, at 90 ° C, for the removal of benzene.

Example 3. Preparation of the Pt / SDB / PTFE catalyst The platinum-coated benzene styrene support, as in Example 1, is softened to dimensions below 0.08 mm and is mixed as homogeneously with teflon powder in relation to table 1: 10, after which it is molded as Raschig rings at pressures between 8 ... 10 at. The obtained rings are then sintered in an oven at 300 ... 320 ° C, preferably 310 ° C.

Table 1 illustrates some of the main characteristics of the catalysts thus prepared.

Table 1

The characteristics of hydrophobic platinum catalysts

Nr. crt. The type of catalyst Specific area (m ² / g) Active platinum surface (m ² / g) The average size of Pt. Â dispersion phase metal H / Pt 1. Pt / C / PTFE 20 213 10 0.80 2. Pt / SDB / PS 565 250 9 0.83

Claims (3)

claims 1. Process for the preparation of hydrophobic platinum catalysts, of the type: platinum / carbon / pol itetrafluoroethylene, 5 platinum / styrene benzene / polystyrene and platinum / styrene benzene / teflon, characterized by the use of hydrophobic media with a large specific surface , 700 ... 900 m ² / g of the styrene type benzene divin and 10 hydrophilic substrates with a particularly large surface area 1200 ... 1700 m ² / g, of the type of activated or super-activated charcoal, which is impregnated with hexaeloroplatinic acid, dissolved in -a solution consisting of two 15 components, a component in which the acid is slightly soluble, acetone and a component in which the hexaeloroplatinic acid is not soluble, benzene, in a volume ratio acetone: benzene of 1: 5 preferably 1: 3, after which the drying of the impregnated substrate is carried out at a temperature below 65 ° C, preferably 55 ... 60 ° C and under vacuum at a pressure of IO ' ¹ ... IO' ² at. to constant mass. 2. Process for preparing the platinum catalyst on styrene benzene polystyrene, according to claim 1, characterized in that it uses, for the purpose of spherical agglomeration, a benzene solution of polystyrene of concentration 1 ... 10%, preferably 5 %. 3. Process for preparing the platinum catalyst divin benzene polystyrene, according to claim 1, characterized in that it uses a mixture of platinum-coated benzene styrene styrene and teflon powder, in a ratio of 1: 10 weight, pressed at 8 at and sintered at 310 ° C.