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34Ni-Cr-Al-Mg CATALYSTS PREPARED BY SOLUTION COMBUSTION SYNTHESI FOR CATALYTIC REFORMING OF METHANE INTO SYNTHESIS GAS
S. A. Tungatarova*^, G. Xanthopoulouc, G. N. Kaumenova^, and T. S. Baizhumanovafl'A
aJSC D.V. Sokolsky Institute of Fuel, Catalysis and Electrochemistry, Almaty, 050010 Kazakhstan
bAl-Farabi Kazakh National University, Almaty, 050040 Kazakhstan
cInstitute of Nanoscience and Nanotechnology, NCSR Demokritos, Athens, 15341 Greece
*e-mail: tungatarova58@mail.ru
DOI: 10.24411/9999-0014A-2019-10179
Preparation of catalysts by solution combustion synthesis is one of the new directions in catalysis. Solution combustion is based on an exothermic redox reaction between soluble salts with organic fuel in an aqueous solution. The effectiveness of this method lies in the simplicity and ease of preparation of catalysts, short reaction time and relatively low cost, and hence the efficiency of the process. The solution combustion method is used in various industries, especially for the preparation of ceramic materials, catalysts, pigments and alloys [1].
Methane is a major component of natural gas. In the future, the conversion of methane to hydrogen and synthesis gas (CO and H2) using heterogeneous catalysts may play an important role in the production of liquid fuels and chemicals. It is known that catalysts based on Ni-Al-Mg exhibit very high activity and selectivity in the partial oxidation reaction [2].
Metal nitrates as the oxidizing agents and glycine as the fuel were used for synthesis of the Ni-Cr-Al-Mg catalysts. The catalysts were prepared by solution combustion synthesis. Nitrate to fuel ratio equal to 1.10 ml of distilled water heated to 80°C was added to the initial mixture of active ingredients for the preparation of catalysts. The resulting mixture was mixed until homogeneous state. The catalysts were placed in a muffle furnace, which was previously heated to 500°C. Figure 1 shows the temperature-time profile of the volumetric mode of combustion for the Ni-Cr-Al-Mg system.
Time, sec
Fig. 1. Temperature-time profile of the volumetric mode of combustion of the Ni-Cr-Al-Mg system.
From the figure it can be seen that evaporation of water followed by gel formation occurred up to 300 s. The combustion temperatures in the lower, middle, and upper parts differed in temperature. At about 375 s, the temperature rose quickly and gas formation was observed. After completion of the preparation process, the beaker with the obtained catalyst was removed
ISHS 2019 Moscow, Russia
from the muffle furnace and cooled at room temperature. The content of nickel and chromium in the catalysts varied from 5 to 35%.
Figure 2 shows the electron microscopic images of the 25% Ni(NO3)2 + 5% Cr(NO3)3 + 10% Al(NO3)3 + 10% Mg(NO3)2 + 50% glycine catalysts.
Fig. 2. SEM images of the 25% Ni(NO3)2 + 5% Cr(NO3)3 + 10% Al(NO3)3 + 10% Mg(NO3)2 + 50% glycine catalyst.
The figure shows that the catalyst is nanoscale. Small bubbles are visible at a magnification, and nanopores are formed during combustion. The activity of catalysts was investigated on a flow catalytic installation with a tubular quartz reactor. In the course of experiment, the influence of space velocity on yield of products, as well as the ratio of initial gases to process parameters, was determined. The composition of the initial reaction mixture: 34% CH4:17% 02:49% Ar. It has been shown that the Ni-Cr-Al-Mg catalysts with different contents of Ni and Cr are active in the partial oxidation of methane. Figure 3 a shows the effect of space velocity on methane conversion in the temperature range from 600 to 900°C. The highest results (methane conversion up to 98% and CH4/O2 ratio = 2) were obtained at GHSV = 2500 h-1. Figure 3b shows the effect of nickel content in catalyst composition on methane conversion in the temperature range from 600 to 900°C at GHSV = 2500 h-1. The best catalytic characteristics were observed for the 25% Ni(NO3)2 + 5% Cr(NO3)3 + 10% Al(NO3> + 10% Mg(NO3)2 + 50% glycine sample on which high CH4 conversion (up to 98%) values were obtained.
Temperature, °C
Fig. 3. Methane conversion on the 25% Ni(N03)2 + 5% Cr(N03)3 + 10% A1(N03)3 + 10% Mg(NO3)2 + 50% glycine catalysts at various space velocities (a) and influence the composition of catalyst on conversion of methane at 600-900°C.
High selectivity for H2 (up to 92.4%) and CO (up to 99.5%) (Fig. 4) was achieved under optimal conditions for the conversion of methane to synthesis gas on the 25% Ni(NO3)2 + 5% Cr(NO3)3 + 10% Al(NO3)3 + 10% Mg(NO3)2 + 50% glycine catalyst, and the ratio of reaction products varied in the range of H2/CO = 1.49-1.87 at 600-900°C.
600 650 700 750 E00 850 900
Temperature, °C
Fig. 4. Effect of process temperature on hydrogen and CO selectivity on the 25% №(N03)2 + 5% Cr(N03)3 + 10% Al(N03)3 + 10% Mg(N03)2 + 50% glycine catalyst.
The study of catalyst on a transmission electron microscope showed that semitransparent plates with small dense particles of 8-10 nm in size are present in the original samples recorded at low magnification. The microdiffraction pattern is represented by reflexes arranged in rings and can be attributed to a mixture of phases of NiO (JCPDS, 4-825), MgO (JCPDS, 4-829), MgNi02 (JCPDS, 24-712), CrO (JCPDS, 8-254). Dense aggregates composed of particles ranging in size from 1 to 5 nm are present on spent catalysts recorded at low magnification. In addition, elastic carbon nanotubes with a diameter from 1 to 2.5 nm are present in the samples.
The work was supported by the Ministry of Education and Science of the Republic of Kazakhstan (AP05132348).
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2. H. Messaoudi, S. Thomas, A. Djaidja, S. Slyemi, R. Chebout, S. Barama, F. Benaliouche, Hydrogen production over partial oxidation of methane using Ni Mg Al spinel catalysts: A kinetic approach, C. R. Chim., 2017, vol. 20, no. 7, pp. 738-746.
