Gunel Azimova

Title : The effect of microwave exposure on the synthesis of ferrite catalysts for oxidation of carbon monoxide

Abstract:

The aim of this work was to study the effect of microwave radiation in the synthesis of cobalt and copper ferrite on their catalytic activity in the low-temperature oxidation of carbon monoxide. The synthesis was carried out by ceramic method from oxides and sol-gel method with combustion. Metal oxides were used as starting materials for the solid-phase synthesis of cobalt and copper ferrite. When synthesizing ferrites by the sol-gel method with combustion, both the solutions of the corresponding salts and the organic reagents (sols) and the resulting gels were subjected to microwave combustion.

The microwave treatment was performed in an EM-G5593V household microwave oven (Panasonic) with a resonator volume of 25 l varying at the magnetron power of 160-900 W with an operating frequency of 2450 MHz. The solid-phase synthesis of ferrite was carried out as follows: metal oxides taken in a certain stoichiometric ratio were homogenized in ethyl alcohol until it dried out completely. Then, the resulting mixture was placed in a quartz beaker and subjected to microwave treatment. Optimal conditions were as follows: magnetron power 800 W, total phase formation time with intermediate grinding of samples 10-15 minutes. 

The synthesis of ferrites by the sol-gel method with combustion was carried out in 2 ways:
The sol or gel was microwaved until the combustion ceased completely, forming a powder within a few minutes. 
The microwave treatment was stopped at the moment of ignition. In the case of the gel this can be done very clearly, even at low magnetron power it takes about 10 seconds. In this case the microwave energy is used for "ignition" without further prolonged irradiation.

The catalytic activity of ferrite samples obtained by the above methods in the oxidation reaction of carbon monoxide was studied. The study of the catalytic activity of the synthesized ferrites showed that the ferrite samples prepared by the sol-gel combustion method with microwave "ignition" are the most active in CO oxidation.  In these samples, the complete conversion of CO to CO₂ occurs at 180-250⁰C temperature. The catalytic activity in the oxidation conversion of carbon monoxide of ferrites obtained by this method is comparable with that of ferrites obtained by the sol-gel combustion method with traditional burning, while the samples with additional afterburning in a microwave oven and samples synthesized from oxides by the solid-phase synthesis in a microwave oven completely convert CO to CO₂ at 280-350⁰C.

Ferrites obtained by solid-phase synthesis from oxides and prolonged gel or sol burning in a microwave oven are characterized by low values of the specific surface, which is associated with the aggregation of the obtained particles as a result of a very rapid temperature rise and a long processing time. Ferrites obtained by microwave "ignition" of the gel have a larger specific surface area and smaller crystallite size, due to which they exhibit higher activity in the oxidation of carbon monoxide to dioxide.

AudienceTake Away:

• In recent years, the traditional methods of obtaining heterogeneous catalysts use different types of exposure, including microwave exposure. Analysis of literature data shows that by applying microwave radiation in the sol-gel method with combustion, it is possible to synthesize nanosized ferrites. However, unlike conventional heating in a muffle furnace, when it is possible to regulate the temperature, i.e., to set a certain temperature regime, in the microwave furnace the parameters to be set are power and time.   The feature of the sol-gel method with combustion is that the beginning of the combustion process is initiated by an external thermal influence, and further the process proceeds due to the heat of the exothermic combustion reaction of the organic component.  Therefore, determining the time of microwave action on the system, along with the nature of the organic reagent, plays a major role in the formation of surface morphology, texture, and dispersity of ferrites, which is extremely important in their use as catalysts for the oxidation of carbon monoxide into dioxide. This study has shown that when producing heterogeneous catalysts by the sol-gel method with combustion, microwave exposure has a positive effect when used as a combustion initiator, but not long exposure.
• The results of this study can be useful for researchers in the synthesis of various inorganic compounds, including catalysts for chemical reactions.
• The information obtained in this study can be used in training in laboratory practice when considering the effect of various physical fields on the synthesis of heterogeneous catalysts.

Biography:

Ph.D. student Gunel Azimova studied Chemistry at the Lankaran State University (LSU), Azerbaijan, and graduated as a chemist in 2015. She then gained the masters degree at Sumgait State University, Azerbaijan. After one year she joined Ph.D. degree supervised by Dr. Sima Zulfugarova in 2018 at the Institute of Catalysis and Inorganic Chemistry of ANAS, Azerbaijan. She has published more than approximately 7 research articles.