WO2002055432A1

WO2002055432A1 - Method of synthesizing of nanosize carbides and active catalysts________________________ _

Info

Publication number: WO2002055432A1
Application number: PCT/AM2001/000009
Authority: WO
Inventors: Razmik Malkhasyan; Tamara Garibyan; Susanna Grigoryan; Sergo Kamanchajyan; Levon Vartikyan; Rita Grigoryan; Varia Minasyan
Original assignee: Razmik Malkhasyan; Tamara Garibyan; Susanna Grigoryan; Sergo Kamanchajyan; Levon Vartikyan; Rita Grigoryan; Varia Minasyan
Priority date: 2001-01-10
Filing date: 2001-08-22
Publication date: 2002-07-18

Abstract

The invention refers to the sphere of material science, nanotechnology and catalysis. The aim of the suggestion invention is to create the method of obtaining of the active nanosize amorphous catalysts and carbides on their basis, to increase the effectiveness and profitableness of the processes of their synthesis. It is worked out the method of obtaining of the amorphous single component metals, putting on the different supporters with the large specific surface. The Indicated metals Mo, W, Cu, etc., as well as their carbides has displayed the high catalitic activity, similar to the metals of platinum group. The applying of the amorphous nanosize metals in the process of their carbidization allowed to lower the temperature and to shorten sharply the time of their synthesis, and just that raises the profitableness of the processes of their synthesis.

Description

Method of synthesizing of nanosize carbides and active catalysts

The inventions refers to the sphere of material science, nanotechnology and catalysis. The different methods of synthesis of the active catalysts and carbides are known. While they obtain the ordinary catalysts by the way of their chemical synthesis, the carbide as a rule are being received as a result of high temperature synthesis at T>800 °C [TexHOJioriDi κaτajra3aτopoB. Tloa pejasuHeft H.π.Myx ieHOBa, JleHHHrpaΛ,, 1979 r.]. However in this case non-nanosize, but coarse powders of these compounds are being received. They obtain the nanosize catalysts and carbides by high temperature method too. For example, in the electric arc, in which one of the electrodes is a given metal, and the other one is made from carbonaceous rod, in combination with the presence of the quenching media as the inert gases [Li Z.Q., Zhang H.F. and col. "Nanostructured materials" 1998 , V 10, N7, pp. 179-184]. However the obtaining carbides contain the crystalline carbone in considerable quantity, that in conjunction with the large expenditures of the energy leads to the lowering of the profitableness of the process. It is known the method of obtaining of the nanosize carbide of Molybdenum Mo₂C by the way of ultrasound decomposition of hexacarbonil of Molybdenum Mo(CO)₆ during 3 hours with its consequent thermal treatment in CH₄ : H flow at 500 °C during 48 hours [Suslick K.S., Hycon I., Fang M. " Nanostructure materials generated by high-intensity ultrasound: Sonochemical synthesis and catalytic studies" // Chem. Mater., 1996, N2, PP 2172-2179.]. The main shortcoming of this method is in use of the expensive initial carbonyls and in long duration of synthesis itself, that also lowers the profitableness of the process.

The other methods of obtaining of the catalysts including the carbides, are also known. However as the catalytic activity is stipulated only by the behavior of the surface layers of the catalyst, including the pores, so the coating of the different supporters (SiO₂, Al₂O , etc.), especially those ones that have a developed specific surface, is the most expedient and effective among the existing methods ["OCHOBM MeτoΛθB

aτajni3aτopoB" B.A.,Zt3Hcκo "Hayxa" HOBOCHBHPCK 1983 r.] The following method is the most close one. They impregnate preliminarily prepared supporter by the salt solution of the corresponding metal, with its following drying at the temperature in 100 °C, then heating it at the temperature that as a rule more than 400 °C in the air atmosphere till the receiving of the oxide and the reduction of the latter by the molecular Hydrogen at the temperatures that higher than 400 °C. Later on, in case of obtaining of carbide they carbidize the reduced metal, passing the mixture Co+H₂ or CH₄ +H₂ through it during 40 or more hours at the temperature 850-900 °C [Keller N.Wehrer P. and col. "Catalytic activity of bulk Tungsten carbides for alkane reforming". // Catalyst today, 1995, N153, p 9-16 and Leclerq L., Prigent M. and cjl. "Tungsten carbide and Tungsten -Molybdenum carbides as automobile exhaust catalysts"// Catalysis and automotive pollution control, 1987, p.417-426.] Such a high temperature and duration of the synthesis lowers the productivity and the profitableness of the process.

The aim of the proposeing invention is to create the method of obtaining of the active nanosize amorphous catalysts and the carbides on their basis as well as to increase the effectiveness and profitableness of the processes of their synthesis. The essence of the method lies in the following. According to the method they obtain the active metallic catalysts and the nanosize carbides by the coating of metal-containing compounds on the supporters which decompose them till oxides and reduce them thermally by the Hydrogen and carbidize by Methane-Hydrogen or CO+H₂, etc, mixtures. Thanks to the invention in order to lower the temperature and the duration of the synthesis, they realize the reduction through the quantum-chemical technology by the excited molecules of Hydrogen with the consequent obtaining of the amorphous nanosize metals which then also carbidize at the lowered temperatures.

The proposing method of obtaining of the active catalysts and carbides is based on the receiving by us fact, that obtained by quantum-chemical technology amorphous powders of metals have nanosize magnitude that on combination with their amorphism leads to the considerable accumulation of the energy in them, just that in the end provides their high catalytic activity. Moreover, the temperature of synthesis and using of catalysts as well as the time of the synthesis of carbides are being reduced sharply with the simultaneous small lowering of the temperature of their synthesis . The essence of the invention is presented by the following examples: the certain quantity of supporter (0,5-1 gr.), in particular γ-Al₂O₃ with specific surface 60 m²/gr in the shape of spherical granules by size on 2-3 mm, preliminarily tempered at 400 °C during 2 hours is being saturated with solution NH₄MoO₄. Then the granules are being dried at temperature 80-100 °C and saturated at 400 °C during 4 hours in the air till the obtaining of the oxide MoO . Obtaining MoO on γ-Al₂O₃ has subjected to quantum-chemical treatment by the excited molecules of Hydrogen at 25-30 °C ( Malkhasyan R.T. Method of synthesizing amorphous metals, Patent Republic of Armenia N417, 1994) till the receiving of the amorphous Molybdenum. Further the sample was being coated by hexen and was testing on catalytic activity in the separate reactor. It was conducted the comparative investigation of the catalysts that were obtained by the method of saturation or by the method of mechanical putting of the amorphous metals that were obtained by the same quantum-chemical method, with the catalysts, which were obtained by the high temperature reduction of the same oxides by the ordinary Hydrogen at the temperature within the framework of 450 °C in the process of oxidizing dehydrogenation of cyclohexane into formaldehyde (Table 1) and on the processes of dehydrogenation of cyclohexane into benzene (Table 2).

In all investigated cases the percentage content of the amorphous metals did not exceed 35% from the total mass of catalyst.

Table 1

Presented on the table 1 results are received at the temperature 260 °C and, as it is seen, conversion is being come nearer to 100%. In order to attain the industrial catalysts at the present it is necessary to raise the temperature of the process almost twice as much, till 500 °C.

Table 2

As it is seen from the Table 2 the amorphous Molybdenum that is obtained after the saturation of MoO₃ is the most active. Obtained by the analogous way amorphous nanosize Molybdenum after the saturation at the temperature 450 °C is being carbonized completely during 6-8 hours instead of 48 hours at 500 °C. [ Suslick K.S. Hycon I., Fang M. "Nanostructured Materials Generated by High-intensity Ultrasound: Sonochemical Synthesis and catalitic studies "// Chem Mater 1996, N2 P.2172-2179]. Obtained by the new method carbides shows the high and stable activity with the invariable 100% selectivity. The analogous results are also obtained on the other metals for example Tungsten W, Iron Fe, etc. The carbides synthesized by the given method are similar to the catalysts of the platinum group by their selectivity and conversion.

Claims

Claim

The method of obtaining of the active metallic catalysts and nanosize carbides in accordance with that they coat metal-containing compounds on the supporters, then decompose till the oxide and reduce thermally by Hydrogen and carbidize by Methane - Hydrogen or other mixture, differing by the following. In order to lower the temperature and duration of the synthesis, they accomplish the reduction by the excited molecules of Hydrogen with the obtaining of the amorphous nanosize metals and the carbides on their basis.