(CuO)x*(CoO)y*(NiO)z*(Fe2O3)k*(MoO3)m/HSZ CATALYZER AND STUDYING IT WITH PHYSICOCHEMICAL ANALYSIS METHODS

ABSTRACT

The analysis of the physicochemical and operational characteristics of two industrial catalysts for the synthesis of nanocarbon has been carried out. Various methods: X-ray phase, chemical, and IR spectroscopy were used to investigate the composition of the catalysts. It was shown that the main component of industrial catalysts is iron molybdate (67.27%). The catalyst contains about 31% МоО₃, and 1-2% of molybdenum oxide is included in the lattice of iron molybdate, forming a solid solution. The presence of acid sites of the type on the surface of the catalysts was detected by IR spectroscopy. Lewis and Bronsted acids are the main centres of varying strength. The catalysts are highly active: their formaldehyde productivity reaches a value (12.5-13 mmol/g.s). The surface area of industrial contacts is (7-9 m²/g); the size of the mesopores is 2-40 nm. Thus, industrial catalysts for the synthesis of nano carbons are of high quality, which ensures their high performance throughout the entire period of operation.

АННОТАЦИЯ

Проведен анализ физико-химических и эксплуатационных характеристик двух промышленных катализаторов синтеза наноуглеродов. Для исследования состава катализаторов использовались различные методы: рентгенофазовый, химический, ИК-спектроскопия. Показано, что основным компонентом промышленных катализаторов является молибдат железа (67,27%). Катализатор содержит около 31 % МоО₃, а 1-2 % оксида молибдена включается в решетку молибдата железа, образуя твердый раствор. Наличие на поверхности катализаторов кислотных центров типа фиксировали методом ИК-спектроскопии. Кислоты Льюиса и Бренстеда являются основными центрами различной силы. Катализаторы обладают высокой активностью: их формальдегидная продуктивность достигает величины (12,5-13 ммоль/г.с). Площадь промышленных контактов составляет (7-9 м²/г); размер мезопор 2-40 нм. Таким образом, промышленные катализаторы синтеза наноуглеродов отличаются высоким качеством, что обеспечивает их высокую работоспособность на протяжении всего периода эксплуатации.

Keywords: Iron molybdate, molybdenum, catalyst, IR spectroscopy, X-ray.

Ключевые слова: молибдат железа, молибден, катализатор, ИК-спектроскопия, рентген.

INTRODUCTION

The influence of various factors on the synthesis of nanocarbon from the walnut peel, apricot kernel, methane, natural gas, and propane-butane fractions was studied, and the texture and sorption characteristics of the obtained nanocarbon were examined [1,2,3]. The catalytic activity of the catalyst containing (CuO)_x*(CoO)_y*(NiO)_z*(Fe₂O₃)_k*(MoO₃)_m/HSZ prepared based on "zol-gel" technology for the implementation of processes was studied under differential reactor conditions [1]. At the same time, the effect of various factors on the rate of formation of nanocarbon obtained from methane, natural gas, and propane-butane fractions was studied and optimal process conditions were proposed [4, 5, 6].

The physicochemical and operational properties of two industrial catalysts for nanocarbon synthesis were analyzed [7]. Different methods: X-ray phase, chemical, and IR spectroscopy studied the composition of catalysts [8, 9, 10].

A detailed microkinetic model and a digital methodology for combining Euler-Euler methods to simulate liquefied bed reactors have been proposed to the industry [11]. Based on laboratory-scale experimental data, low losses (less than 10%) are achieved [12,13,14]. In general, the work leads to the introduction of detailed kinetics in the simulation of industrial liquefied reactors [15,16].

EXPERIMENTAL PART

The activity of the iron-molybdenum oxide catalyst depends on the ratio of the initial salts and the calculated catalyst composition of the oxides to Fe₂O₃ and MoO₃. The active ensembles of the iron-molybdenum catalyst in the structure are tetrahedral {FeO₄ ∙MoO₄} and the less active polyhedral ensembles are: {FeO₄ ∙MoO₆}, {FeO₆ ∙MoO₄} and {FeO₆ ∙MoO₆}. The tetrahedron with the highest catalytic activity in the catalyst is represented by the scheme of electrons formed due to the redistribution of its oxidation number:

                                              (1)

The position of the tetrahedron shown on the right is determined using EPR spectra. The catalyst in the form of a general formula can be written as aFe₂O₃∙bMoO₃. The maximum value was determined by optimizing the composition of this catalyst. In it, the catalytic activity is better manifested in a catalyst containing Fe₂O₃∙ 2MoO₃. The amount of molybdenum in such a catalyst is as follows:

                                                    (2)

As a result of experimental studies, the catalyst, which contains about 62% by mass, was found to have maximum activity. The consistency of the calculations means that the theoretical and experimental values are considered satisfactory. The method and theory of multi-faceted catalysis for optimizing the composition of complexes show the wide possibilities of the thermodynamics of oxide catalysts. The addition of Fe₂O₃ to MoO₃ leads to increased inactivity.

Mo: Fe = 1.7 in proportion to the composition of the femur, up to the atomic ratio. Subsequent enrichment with iron leads to a progressive decrease. Iron molybdate [Fe₂(MoO₄)₃] is an active catalyst. In some studies, the surface in octahedral coordination binds Mo atoms to active centres. The stoichiometric value for a catalyst larger than the atomic ratio Mo: Fe is consistent with the finding of maximum activity. This coordination allows molecules that are double-bonded to Mo to react. This means that methanol must be bonded at two points near the surface at the same time.

RESULTS AND THEIR DISCUSSION

The specific catalytic activity of iron-molybdenum catalysts has been shown to increase with increasing molybdenum content. A catalyst with an atomic ratio of Mo: Fe = 2.2 is almost as active as [Fe₂(MoO₄)₃] and as pure and selective as MoO₃. To do this, excess molybdenum oxide is needed to maintain the stoichiometric composition of the surface during the experiment. According to the results of thermogravimetry, radiography, and IR spectroscopy, this mainly occurs when new reagents enter the catalytic layer.

Figure 1. Nitrogen adsorption and IR spectra of Fe₂(MoO₄)₃ and Fe₂(MoO₄)₃*MoO₃ catalysts

The Lewis acid centre consists of surface metal cations with free bonds, and the Bronsted acid centre is the Lewis acid centre that has absorbed water. The main centres are oxygen anions, which are located on the surface. The presence of Lewis centres was confirmed by absorption bands in IR spectra (1210, 1250, 1620 cm^-1) and Bronsted centers (1445, 1400 cm^-1) characterizing coordinated ammonia (Figure 1). A scheme of catalyst formation by heat treatment at room temperature using NMR and EPR spectra of samples of different compositions and different processing was proposed. Thus, at temperatures of 500 °C and above, when MoO₃ is in excess, iron molybdate enters the cavities of the grid without significant changes. The higher the washing temperature, the more solid solution is formed, but at 750 ℃ the decomposition of molybdate is observed. Increasing the amount of molybdenum in the catalyst increases the stability, but slightly reduces the specific activity. However, in the ratios of Mo: Fe = 1.7: 2.5, the activity does not change significantly, and the stability leads to a significant increase. Therefore, it is preferable to use a catalyst with a Mo/Fe ratio of Mo: Fe = 2.5: 1 as the basic case for the industry. Given the slow volatility of molybdenum, it is desirable in the industry to increase its atomic ratio from 2.4 to 2.6. Activity and selectivity are observed in both catalysts.

Figure 2. Sample current spectra of 2.3% MoO₃ /Fe₂O₃ (a) LEIS 1 mA and Fe /Mo intensity during spraying (b)

The first LEIS scan (a) belongs to the Mo signal, and the Fe signal is not present. This reveals the outermost surface layer. Digital integration provides a limited value for this region, however, extrapolation confirms that a complete monolayer has been achieved for the 2.3% MoO₃ /Fe₂O₃ catalyst, ensuring that the Mo /Fe intensity ratio is accurate to zero (Figure 2).

Figure 3. X-ray spectral results of Fe₂O₃: NiO: CuO oxides at cat №1 and cat №2 at 600-800 K

Spectral results of atoms in catalysts cat №1 and cat №2 were obtained using an XRD diffractogram. In this case, the 25^o, 35^o, 44 ^o, 55^o, 58^o, and 66 ^o waves in the 2θ are related to the Fe₂O₃ phase. Furthermore, the NiO phase is represented by the 37,4^o, 64,3^o, 75,3^o, and 79^o peaks in the 2θ. NiO and CuO have their peaks that overlap. The oxides are a mixture of (Ni(_1-x)-Cu_xO) (Figure 3).

Figure 4. The effect of temperature and pressure on the phase composition of iron molybdate over 3 hours

Temperatures for hydrothermal treatment: 100 ℃; 150 ^оC;200 ℃. Indexed phases: a-МоО₃; b-Fе₂О₃; c-Fе₂(МоО₄)₃

CONCLUSION

The analysis of the physicochemical and operational characteristics of two industrial catalysts for the synthesis of nanocarbon is carried out. Various methods: X-ray phase, chemical, and IR spectroscopy were used to investigate the composition of the catalysts. It was shown that the main component of industrial catalysts is iron molybdate (67.27%). The catalyst contains about 31% МоО₃, and 1-2% of molybdenum oxide is included in the lattice of iron molybdate, forming a solid solution. The presence of acid sites of the type on the surface of the catalysts was detected by IR spectroscopy.

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