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ISSN 2522-1841 (Online) AZERBAIJAN CHEMICAL JOURNAL № 3 2022 ISSN 0005-2531 (Print)
UDC 544.4:544.47:544.344
Fe-CONTAINING CARBON NANOTUBES AS CATALYSTS IN THE AEROBIC OXIDATION REACTIONS OF DECALIN AND TETRADECANE
N.A.Mustafayeva
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
Received 13.01.2022 Accepted 08.02.2022
This artide studies the catalytic activity of mufti-watted carbon nanotubes (MWCNTs) in the oxidation reactions of aliphatic and polycyclic hydrocarbons is studied. In order to determine the catalytic activity, MWCNTs catalysts containing 22.8% Fe each were used. Catalyst samples were synthesized from propane gas under optimal conditions determined by CVD method. The experiments were performed at 5 different temperatures (60, 80, 100, 120, 1400C) for 2 hours. No significant change in the oxidation reaction of both hydrocarbons was observed at rdativefy tow temperatures. In the oxidation of decalin, when the reaction temperature rises to 1200C and 1400C, oxidation has afteady taken piace, and the rate of the reaction is directly proportional to the increase in temperature. The same trend can be seen in the oxidation reaction of tetradecane at MWCNTs with temperatures of 120 and 1400C. However, unlike decalin, the MWCNTs sample in tetradecane oxidation showed optimal catalytic performance at 1200C. However, at these temperatures, where oxidation occurs, the oxidation of decalin and tetradecane in an environment without a catalyst is almost non-existent.
Keywords: MWCNTs, CVD method, catalyst, decalin, tetradecane, kinetic parameters, liquid phase oxidation of hydrocarbons, nanocatalysis, catalytic activity, propane.
doi.org/10.32737/0005-2531-2022-3-87-92
Introduction
For the first time, the importance of catalytic processes with the introduction of catalysts into chemical processes in industry [1-3]. Catalytic processes have a great impact on our way of life and make a great contribution to the world economy. According to some estimates, catalysis accounts for more than a third of the world's gross domestic product [4-6]. Much of this activity has been concentrated in several major chemical industries, including crude oil refining and the synthesis of major commodities such as ammonia, sulfuric acid, methanol, propylene, ethylene oxide, and acetic acid.
With very few exceptions, all of these systems use heterogeneous catalysts [7]. Heterogeneous catalysts are more efficient in terms of ease of management, separation from the reaction mixture, recovery and reuse due to their molecular analogues. In addition, heterogeneous catalysts simplify processes in the reaction medium with properties such as good stability, low toxicity and insolubility, as well as functionality [7]. Homogeneous catalysis, on the other hand, has a number of disadvantages
and costs, including additional separation and purification steps. For example, many pharmaceutical products are made using highly toxic metal-organic catalysts, which must be completely removed from the final product, which significantly increases the cost of the synthetic process. Instead, many of these problems can be prevented by using heterogeneous catalysts [7].
Currently, the most widely used industrial catalysts are materials containing activated carbon (AC) or various precious metals impregnated on zeolites [8-12]. In addition, due to their many important physicochemical properties [13, 14], nanostructured carbon materials may be excellent alternatives such as catalyst support. The possibility of large-scale production of multi-walled carbon nanotubes (MWCNTs) has recently increased its use in catalytic processes [15]. For example, palladium nanoparticles impregnated on MWCNTs (Pd/MWCNTs) are an effective catalyst for the hydrogenation of le-vulinic acid from biomass [16]. Therefore, they are preferred for use as a support material in heterogeneous catalysis [17].
In [18] the study developed catalysts containing 5% by weight of metal (Pd, Rh, Ru, and Ir) and used nitrogen-free multi-walled carbon nanotubes (MWCNTs) and N-containing carbon nanotubes (N-MWCNTs) as supporting materials. The prepared catalytic samples were used in the hydrogenation reaction of 1-octa-decene and the catalytic activities were compared. Maximum octadecene conversion was 96.5% on the Rh/MWCNTs catalyst after 80 minutes, and 95.5% after two hours in the presence of Pd/MWCNTs. The same conversion with Pd/N-MWCNTs was 94.4% after 80 minutes of hydrogenation, and in Rh/N-MWCNTs it was 95% after two hours. The most active catalysts were found to be nanotubes modified with palladium and rhodium. The catalytic activities of the samples are as follows: Pd/CNTs=Rh/MWCNTs>Pd/MWCNTs> Rh/CNTs> Ir/MWCNTs>Ru/CNTs>Ir/CNTs>Ru/MW CNTs.
Overall, palladium, with N-bamboo-like carbon nanotubes, is the most promising catalyst in the sample collection. N-containing CNTs have many applications, including hydrogenation [19] and dehydrogenation potential [20], oxidation reactions [21], Fisher-Tropsch synthesis [22], and hydro-desulfurization [23]. The selective hydrogenation of nitrobenzophe-none to aminobenzophene by a catalyst sample (Pd/N-CNTs) obtained by modifying nitrogen and the same metal nanoparticles in modern CNTs was investigated, as a result, Pd/N-CNTs were more selective than Pd/CNTs and the added carbon supplement Pd was aminoben-zophenone [24]. In addition, Pd/N-CNTs are promising catalysts for selective reductions of cinnamaldehyde [25, 18].
All these arguments lead to the synthesis of new types of heterogeneous catalysts with high catalytic activity and selectivity, as well as the ability to compete with homogeneous catalysts. Recently, the development of nanotechnology and the synthesis of new nanomaterials has made the development of such catalysts very relevant [7]. In this regard, in this article, we present our research on the synthesis of nano-sized heterogeneous type catalysts and the study of their catalytic activity.
In our previous study, multi-walled carbon nanotubes were synthesized from the liquid and gas phases, and their catalytic activity was studied in the oxidation reaction of aromatic hydrocarbons.
In this study, the oxidation reactions of tetradecane and decalin, respectively, as representatives of alpha and polycyclic hydrocarbons in the presence of Fe-containing multi-walled carbon nanotubes catalysts synthesized from the gas phase were studied.
Experimental part
In our previous study, it was found that MWCNTs samples show high catalytic activity in oxidation reactions, depending on the amount of iron they contain. Multi-walled carbon nano-tubes were synthesized from propane-butane gases that can be produced in multi-tonnage in Azerbaijan and the obtained MWCNTs were studied by XRD analysis method (Figure 1). X-ray diffraction (XRD) analysis of the catalyst was recorded using an X-ray diffractometer (Brooker D2) with a Cu radiation source in the range of -3 to 1470 2Theta. The XRD spectral image revealed that the MWCNTs catalyst contained Fe carbides and a- y-modified Fe atoms. It should be noted that iron atoms have passed through ferrocene, which is a precursor to the synthesis of MWCNTs.
In our study, we focused on the study of the catalytic activity of MWCNTs containing 22.8% iron in the oxidation reactions of polycyclic and alpha-type hydrocarbons.
The amount of iron atom in the MWCNTs was calculated by a method known in the literature [26]. In the experiments, decalin was used as a polycyclic hydrocarbon and tetradecane was used as an aliphatic hydrocarbon. The oxidation process was carried out in a laboratory in a gasometric device, and experiments were carried out taking into account two main parameters (the effect of the catalyst and temperature). The rate of the oxidation reaction was measured by the volumetric method, based on the rise of the liquid level in the burette by the absorption of oxygen in the air.
Fig. 1. XRD spectral image of MWCNT catalyst sample synthesized from propane gas in gas phase (Fe = 22.8%, X-ray diffractometer Bruker D2)
Conclusion and discussion
In order to determine the catalytic activity, oxidation reactions of decalin and tetradecane were carried out in the presence of MWCNTs catalysts, each containing 22.8% Fe. The experiments in Figures 2 and 3 show the effect of the catalyst on the reaction rate. Kinetic graphs show that the MWCNTs catalyst sample had a positive catalytic effect on the oxidation reaction of both decalin and tetradecane. According to the results obtained, the catalytic activity in the oxidation reactions of both decalin and tetradecane is due to the presence of Fe compounds in the MWCNTs.
It was found that the reaction temperature had a significant effect on the catalytic performance of the catalyst (Table). Oxidation reactions at temperatures of 60, 80, 100, 120, and 1400C were studied for 2 h. No significant change in the oxidation reaction of both hydrocarbons was observed at relatively low temperatures. In the oxidation of decalin, when the reaction temperature rises to 1200C and 1400C, it is possible to see that oxidation has
already taken place, and that the rate of the reaction is directly proportional to the increase in temperature. However, at both temperatures, a long period of induction was observed at the beginning of the reaction. Given that the reactions take place by a free radical mechanism, this can be explained by the formation of hydroperoxide in the medium, the formation of radicals by decomposition after reaching a certain concentration, and finally the onset of oxidation.
Thus, in the catalytic oxidation reaction of Decalin, the MWCNTs catalyst demonstrates optimal catalytic performance at 1400C. The same trend can be seen in the oxidation reaction of tetradecane at CNTs with temperatures of 120 and 1400C. However, unlike decalin, the MWCNTs sample in tetradecane oxidation shows optimal catalytic performance at 1200C. It should be noted that at these temperatures, where oxidation occurs, the oxidation of decalin and tetradecane in a catalyst-free environment is very small.
Fig. 2. Kinetic dependences of oxygen absorption in the liquid phase of decalin in aerobic oxidation reaction at 120 and 1400C in the presence of MWCNTs catalysts synthesized from propane gas.
Fig. 3. Kinetic dependences of oxygen absorption in the liquid phase of tetradecane in aerobic oxidation reaction at 120 and 1400C in the presence of MWCNTs catalysts synthesized from propane gas.
Results of the oxidation reaction of decalin and tetradecane at different temperatures
Hydrocarbons Temperature, 0C Time, hours Catalytic activity
Without catalysts Decalin 60 2 -
80 2 -
100 2 -
G CVD-1 120 2 +
140 2 +
Without catalysts Tetradecane 60 2 -
80 2 -
100 2 -
G CVD-1 120 2 +
140 2 +
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Fe-TORKÍBLÍ KARBON NANOBORULAR KATALÍZATOR KÍMÍ DEKALÍN VO TETRADEKANIN
AEROB OKSÍDLO§MO REAKSÍYALARINDA
N.O.Mustafayeva
Maqalada alifatik va politsiklik karbohidrogenlarin oksidla§ma reaksiyalarinda goxdivarli karbon nanoborularin (CDKNB) katalitik aktivliyi öyranilmi§dir. Katalitik aktivliyi müayyan etmak ügün har birinin tarkibinda 22.8% Fe olan CDKNB katalizatorlarindan istifada edilmi§dir. Katalizator nümunalari CVD üsulu ila müayyan edilmi§ optimal §araitda propan qazindan sintez edilmi§dir. Eksperimentlar 5 müxtalif temperaturda (600C, 800C, 1000C, 1200C, 1400C)
2 saat arzinda hayata kegirilib. Nisbatan a§agi temperaturlarda har iki karbohidrogenin oksidla§ma reaksiyasinda hiss edila bilacak bir dayi§iklik mü§ahida olunmami§dir. Dekalinin oksidla§masinda reaksiya temperaturu 1200C va 1400C-ya yüksaldikda isa artiq oksidla§manin ba§ verdiyini, temperaturun artmasi ila reaksiyanin süratinin düz mütanasib oldugu mü§ahida olunmu§dur. Eyni tendensiyani tetradekanin QDKNB i§tirakinda 1200C va 1400C temperaturlarda oksidla§ma reaksiyasinda gormak mümkündür. Lakin dekalindan farqli olaraq tetradekanin oksidla§masinda QDKNB nümunasi optimal katalitik aktivliyi 1200C-da ozünü gostarib. Halbuki, oksidla§manin ba§ verdiyi bu temperaturlarda dekalinin va tetradekanin katalizatorsuz mühitda oksidla§masi demak olarki ba§ vermir.
Agar sozlzr: QDKNB, CVD metodu, katalizator, dekalin, tetradekan, kinetik parametrbr, karbohidrogenbrin maye fazada oksidh§masi, nanokataliz, katalitik aktivlik, propan.
Fe-СОДЕРЖАЩИЕ УГЛЕРОДНЫЕ НАНОТРУБКИ, КАК КАТАЛИЗАТОРЫ В РЕАКЦИЯХ АЭРОБНОГО ОКИСЛЕНИЯ ДЕКАЛИНА И ТЕТРАДЕКАНА
Н.А.Мустафаева
В работе исследуется каталитическая активность многослойных углеродных нанотрубок (МУНТ) в реакциях окисления алифатический и полициклических углеводородов. Катализаторы МУНТ, каждый из которых содержит 22.8% Fe, использовали для определения каталитической активности. Образцы катализаторов были синтезированы из газообразного пропана при оптимальных условиях, определенным методом ХОГФ. Эксперименты проводились при 5 различных температурах (60, 80, 100, 120, 1400С) в течение 2 ч. Существенных изменений реакции окисления обоих углеводородов при относительно низких температурах не наблюдалось. При окислении декалина при повышении температуры реакции до 120 и 1400С окисление уже произошло, и скорость реакции прямо пропорциональна повышению температуры. Такую же тенденцию можно наблюдать в реакции окисления тетрадекана на МУНТ с температурами 120 и 1400С. Однако, в отличие от декалина, образец МУНТ в реакции окисления тетрадекана показал оптимальную каталитическую активность при 1200С. Однако при этих температурах, окисление декалина и тетрадекана без катализатора практически не происходит.
Ключевые слова: МУНТ, CVD-метод, катализатор, декалин, тетрадекан, кинетические параметры, жидкофазное окисление углеводородов, нанокатализ, каталитическая активность, пропанa.
