Conversion of model C6-C9 alkanes and straight-run gasoline over Pt(0.1%)-Fe(5%)/Al2O3 catalysts promoted with various additives published by Ural Federal University eISSN 2411-1414; chimicatechnoacta.ru LETTER 2022, vol. 9(3), No. 20229308 DOI: 10.15826/chimtech.2022.9.3.08 1 of 5 Conversion of model C6–C9 alkanes and straight-run gasoline over Pt(0.1%)-Fe(5%)/Al2O3 catalysts promoted with various additives Arai K. Zhumabekova a , Lyazzat K. Tastanova b* , Raigul O. Orynbassar c , Yermek A. Aubakirov c , Elvira B. Zhunusova a a: Chemistry, Chemical Technology and Ecology Department, Kazakh University of Technology and Business, Nur-Sultan 010000, Kazakhstan b: Chemistry and Chemical Technology Department, K. Zhubanov Aktobe Regional University, Aktobe 030000, Kazakhstan c: Department of Physical Chemistry, Catalysis and Petrochemistry, Al-Farabi Kazakh National University, Almaty 050040, Kazakhstan * Corresponding author: lyazzatt@mail.ru This paper belongs to the CTFM'22 Special Issue: https://www.kaznu.kz/en/25415/page. Guest Editors: Prof. N. Uvarov and Prof. E. Aubakirov. © 2022, the Authors. This article is published in open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract Growing demand for hydrogen promotes the research devoted to the development of new catalysts for hydrocarbons processing in ab- sence of H2 or at its low concentration. In the present work, it was shown that during the conversion of straight-run gasoline on a zeo- lite-containing polyfunctional catalyst in a hydrogen-free environ- ment cracking, dehydrogenation, isomerization and alkylation take place due to the redistribution of H2 between initial and formed products directly on the catalyst surface. Fine particles (≤50 Å) local- ize in zeolite cavities and pores of aluminum oxide, while larger ones are on their outer surface. Keywords C6–C9 n-alkanes straight-run gasoline zeolite-containing catalyst modification additives Received: 25.06.22 Revised: 18.07.22 Accepted: 18.07.22 Available online: 26.07.22 Key findings ● High-octane gasoline containing 62.4% isoalkanes and 2.3% aromatic hydrocarbons is obtained on zeolite-containing catalyst at 350 °C with H2:feedstock ratio = 200:1. ● Decrease in H2:feedstock ratio to 50 leads to increase of hydrocracking direction, formation of aromatic hydrocarbons and olefins as well as C10–C13 isoalkanes obtained as a result of a disproportionation reaction. ● Decrease in H2:feedstock ratio leads to essential change in the composition of straight-run gasoline. The presence of aromatic hydrocarbons and olefins, which are octane-forming components, increases the motor properties of gasoline. C10–C13 isoalkanes are the components of diesel fuel. 1. Introduction Many processes at petrochemical and chemical plants are based on the use of hydrogen or hydrogen-containing gas (HCG) [1–3]. Due to the rapid growth of hydrogen energy application, the shortage and cost of hydrogen are increas- ing [4–8]; therefore, reducing the consumption of HCG by developing new catalysts and technologies is urgently needed [9–11]. In the literature [12–16] there are data on transfor- mation of model n-alkanes over Pt/zeolite catalysts. Dur- ing n-octane conversion on Pt/HY catalysts (t = 300 °С, P = 0.18 MPa, H2/octane ratio is 16 mol.%), selectivity of isomers formation rises from 16.0% (0.02% Pt) up to 80.6% (10% Pt) with increasing platinum concentration. Under these conditions cracking direction decreases from 82.2 to 20.6% [17]. It was shown, that conversion of n-hexane over 0.3% Pt-containing zeolites of L and eryonite (E) type is influ- enced by the degree of ion exchange of K+. Under the same conditions (t = 400 °C), the conversion of n-hexane in- creases from 26.1 to 47.0% with an increase in the degree of ion exchange from 17.0% to 82.0% in L zeolite. Accord- ing to NH3 adsorption, three types of acid centers with binding energy (q) equal to 100, 110 and 120 kJ/mol were determined in the catalyst. The highest activity in the n- hexane isomerization reaction is typical for the centers with q = 120 kJ/mol, while the acid centers with lower http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2022.9.3.08 mailto:lyazzatt@mail.ru http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0001-6743-8953 https://orcid.org/0000-0002-9236-5909 https://orcid.org/0000-0002-6198-3018 https://orcid.org/0000-0001-5405-4125 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2022.9.3.08&domain=pdf&date_stamp=2022-7-26 Chimica Techno Acta 2022, vol. 9(3), No. 20229308 LETTER 2 of 5 binding energy also participate in hydro isomerization but with low efficiency [18]. Molecular sieve effect was shown when comparing the properties of catalysts containing L and E zeolites. On L-zeolite with wide pores (0.71 nm) isomer yield is greater than on E-zeolite with narrowpores (0.36x0.52 nm). In the latter case, the pores are not acces- sible to branched isomers. In the present work, conversion of C6–C9 n-alkanes on Pt-Fe/Al2O3+HZSM catalyst modified with additives of ce- rium, molybdenum and phosphorus in the presence of H2 was studied. Processing of straight-run gasoline was carried out with varying content of hydrogen and in its absence. 2. Experimental The catalyst was prepared by impregnation of the Al2O3+HZSM mixture with water solutions of Fe(NO3)3∙9H2O, (NH4)6Mo7O24∙4H2O, Ce(NO3)3∙6H2O, H2PtCl6 and other salts. The wet catalyst sample was formed into granules, dried at 100–250 °C for 5 hours with a heating rate of 20–30 °C/min and calcined at 500 °C for 5 hours. The tatalyst was studied in the reaction of transfor- mation of C6–C9 n-alkanes and straight-run gasoline on the laboratory flow-through unit at the temperatures varying from 280 °C up to 400 °C, the hydrogen pressure of 2MPa, the H2/feed ratio of 200/1, 50/1 and 0/1, and the volume feed rate of 5 h–1. Hydrocarbon composition of the reaction products was analyzed on a "Chrom-4" chromatograph with a stainless steel column filled with γ- aluminum ox- ide by "Supelco". Argon was used as a carrier gas. 3. Results and discussion The conversion and direction of C6–C9 n-alkanes transfor- mation on the Pt(0.1%)-Fe(5%)/Al2O3+HZSM catalyst modified with various additives is affected by the process temperature under otherwise equal conditions (PH2 = 2MPa, V = 5 h–1, H2/feedstock ratio = 200/1). Table 1 shows the results obtained at n-nonane processing. As the temperature rises from 300 to 400 °C, the conversion of n-nonane increases from 51.2 to 93.6%. As shown in Table 1, the olefins formed during dehy- drogenation of intermediate activated surface complexes are rapidly isomerized through the carbonium ion for- mation and hydrogenated to isoalkanes. Due to this, only tracess of olefins are present in the products mixture. Other directions of olefins transformation probably in- clude formation of aromatic hydrocarbons (0.1–2.7%) at temperatures of 350–400 °С. The maximum yield of C4–C8 isoalkanes (35.7%) is determined at 350 °C. The assumed mechanism of alkane conversion is possible on the active catalyst sites containing both metal and acid centers. Figure 1 presents the data on C6–C8 n-alkanes conversion on the Pt-Fe/Al2O3+HZSM catalyst promoted by different additives and the yield of isomers at different temperatures. With the increase in temperature, conversion of n- alkanes grows, and at 400 °C it reaches 96.7–97.9%. The temperature dependence of maximum yield of isomers is observed at close conversion degrees of C6–C8 n-alkanes. The curves pass through the extrema at 350–380 °C. The maximum yield (%) decreases in the following series: hexane (32.0%) > heptane (30.6%) > octane (30.3%). In the high temperature area (>350 °C) the formation of ar- omatic hydrocarbons (0.1–2.8%) and olefins (tracess) is observed. Physical and chemical properties of the polyfunctional, promoted with additives, Pt (0.1%)-Fe(5%)/Al2O3+HZSM catalyst were studied by BET, XRD and electron microsco- py (EM) methods. The specific surface area and total pore volume of the catalyst are 179.2 m2/g and 0.40 cm3/g, re- spectively. The XRD results show that the catalyst is dis- persed. HZSM structural elements (reflexes 12.5; 10.9; 9.8; 3.83; 3.70; 3.64; 2.96 Å), Се (reflex 2.76 Å) (ASTM 38-763), Pt (superimposed with γ-Al2O3, reflex 2.27 Å) (ASTM 4-802), ε-Fe2O3 (1.46 Å) (ASTM 16-895), γ-Al2O3 (reflexes 2.40; 1.98; 1.40) are present. Table 1 Influence of temperature on n-nonane conversion on zeo- lite-containing Pt-Fe/Al2O3 catalyst (P = 2 MPa, V = 5 h –1, H2/feedstock ratio = 200). Products composition, % Temperature, 0С 300 320 350 380 400 С1–С3 hydrocar- bons 1.8 10.9 20.7 34.3 36.5 С4–С9 isoalkanes 20.2 30.9 35.7 33.2 31.5 С4–С8 n-alkanes 29.2 29.4 26.1 23.8 22.9 olefins traces traces traces traces traces aromatic hydro- carbons – traces 0.1 0.2 2.7 Feedstock 48.8 28.8 17.4 8.5 6.4 n-nonane conver- sion, % 51.2 71.2 82.6 91.5 93.6 Figure 1 Influence of temperature on C6–C8 n-alkanes conversion and yield of isomers (P = 2 MPa, V = 5 h–1, H2:feed = 200:1). 1, 4 – Isoalkanes yield and conversion of n-hexane. 2, 5 – Isoalkanes yield and conversion of n-heptane. 3, 6 – Isoalkanes yield and conversion of n-octane. Chimica Techno Acta 2022, vol. 9(3), No. 20229308 LETTER 3 of 5 The EM study (120000 magnification) showed the presence of an aggregate in the Pt-Fe/Al2O3 catalyst modi- fied with cerium, molybdenum and phosphorus, which consists of dense particles of ~200 Å size. The micro dif- fraction pattern is represented by two rings and can be attributed to Fe2O3 Hematite (ЈCPDS, 35-664). At low magnification, large elastic lamellar crystals with basal reflections on their bends were detected. The micro dif- fraction pattern can be attributed to FeOOH (JCPDS, 26- 792). Small loose clusters of dispersed particles with sizes of 20 Ǻ were found in the sample; according to the micro diffraction pattern, they represent CeO2 (JCPDS, 34-394). Small loose clusters of ~100 Å particles give a diffraction pattern which can be attributed to a mixture of Pt3O4, Mo9O26 (ЈCPDS, 21-1284) and CeAlO3 (ЈCPDS, 28-260). Characteristic extensive clusters of 30–40 Å particles of Ce6O11 were detected. An aggregate of loose small particles 30–50 Å in size was found, which is a mixture of Се(MoO4)2, Се2Mo3O12 and PtO2 (ЈCPDS, 57-330). The sam- ple also contains individual large dense crystals with cut features represented by the reflections with hexagonal arrangement, and they are related to FeMoO4, CeP, β-MoO3 (ЈCPDS, 37-1445), and PtO2 (ЈCPDS, 23-1306). Nanosized (20–100 Å) homo- and heteroatomic clus- ters were found in the zeolite-containing Pt(0.1%)- Fe(5%)/Al2O3 catalyst modified with phosphorus, molyb- denum, and cerium additives. In the calcined catalyst (t = 500 °С), platinum (d = 30–100 Å) and iron (d = 200 Å) are in the form of oxides. Iron and cerium (d = 20–50 Å) interact with molybdenum, forming precur- sors (FeMoO4, CeMoO4, Ce2Mo3O12), which transform into heteroatomic Fe–Mo and Ce–Mo nanoclusters in reducing medium. Analysis of the obtained data on dimensionality and structure of metal particles of the catalyst active phase allows us to conclude that it is possible to synthesize nanocatalysts with given composition and properties by directed selection of precursors. Presence of phosphorus in the catalyst prevents the formation of heteroatomic Pt–Fe, Pt–Mo clusters, whereas the introduction of molybdenum into the catalyst composi- tion in the absence of phosphorus increases the dispersion of metal particles and promotes the formation of heteroa- tomic highly dispersed clusters at calcination. However, it cannot be excluded that such heteroatomic clusters may be formed during the hydrogen treatment of the catalyst (350–400 °C). Metal nanoparticles are localized in the cavity and mouths of zeolite and pores of aluminum oxide. In addition, larger 100–200 Å crystals were detected by electron microscopy method on the smooth surface of zeo- lite. It is known from the literature [19, 20] that reduction of iron (III) into iron (II) and iron (0) is observed under hydrogen treatment of air calcined Pt–Fe/Al2O3 – systems [19]. The formation of Pt–Fe clusters, which facilitates and accelerates the reduction of iron, was detected by NGRS method [20]. Zeolite-containing Pt(0.1%)-Fe(5%)/Al2O3-catalyst a modified with additives (Mo, Ce, P) were studied in the process of straight-run gasoline hydro refining at varying temperatures (280–400 °С), and H2:feed ratio (pressure – 2 MPa, V = 5 h–1). At temperature rise from 280 up to 400 °С (РН2 = 2 МPa, V = 5 h–1, Н2:feed=200:1), it was shown, that hydrocracking, hydro isomerization and dehydrocy- clizationare occur on the catalyst at hydro refining of straight-run gasoline. The formation of light C1–C3– hydrocarbons occurs at t≥350 °C, and at 400 °C their yield is 17.6% (Table 2). The optimum yield of C4–C9 iso- alkanes, 62.4%, was determined at 350 °C. At lower and at higher temperatures the yield of C4–C9 isoalkanes de- creases to 50.5 and 51.3%. C10–C13 isoalkanes – 15.6%, C4–C9 n-alkanes – 15.3%, C10–C13 n-alkanes – 0.5% and aromatic hydrocarbons – 2.3% are also present in the product mixture. Olefins appear (0.3–0.4%) at tempera- tures ≥380 °C. At straight-run gasoline hydro refining, attention was paid to the influence of H2:crude ratio on the direction of the process. The data on straight-run gasoline conversion on the Pt-Fe/Al2O3 zeolite-containing catalyst at H2:feed=50:1 are presented in Table 3. In this case, the process was carried out in the temperature range of 350– 400 °C. The maximum hydro refining of straight-run gasoline occurs in these conditions. It follows from Table 3, that with H2:feed ratio decreasing to 50/1 the isomer- izing activity of the catalyst decreases from 62.4 to 54.3%. Table 2 Conversion of straight-run gasoline on zeolite-containing Pt-Fe/Al2O3 catalyst (P = 2 MPa, V = 5 h –1, H2:feed=200:1). Products composition, % Process temperature, 0С 280 300 320 350 380 С1–С3– hydrocarbons – – traces 3.9 10.9 С4–С9 isoalkanes 50.5 54.7 56.7 62.4 54.2 С10–С13 isoalkanes 20.4 19.5 19.7 15.6 13.8 С4–С9 n-alkanes 26.9 23.3 21.1 15.3 18.7 С10–С13 n-alkanes 0.3 0.6 0.7 0.5 traces aromatic hydrocarbons 1.9 1.9 2.0 2.3 2.1 olefins – – traces traces 0.3 Liquid phase yield 100 100 100 96.1 89.1 Table 3 Conversion of straight-run gasoline on zeolite-containing Pt-Fe/Al2O3 catalyst (P = 2 MPa, V = 5 h –1, H2:feed=200:1). Products composition, % Process temperature, 0С 350 380 400 С1–С3– hydrocarbons 6.3 12.4 21.8 С4–С9 isoalkanes 54.3 49.9 42.5 С10–С13 isoalkanes 23.5 20.5 16.9 С4–С9 n-alkanes 8.1 9.9 11.6 aromatic hydrocarbons 7.5 6.9 6.7 olefins 0.3 0.4 0.5 Liquid phase yield 93.7 87.6 78.2 Chimica Techno Acta 2022, vol. 9(3), No. 20229308 LETTER 4 of 5 Hydrocracking with formation of C1–C3 hydrocarbons increases from 3.9 to 6.3% at 350 °C. However, at a re- duced H2:feed ratio the yield of C10–C13 isoalkanes rises from 15.6 to 23.5% (350 °C). In all studied temperature range the yield of C10–C13 isoalkanes is higher than at H2:feed ratio = 200:1. The detected effect of a significant increase in the yield of aromatic hydrocarbons from 2.3 to 7.5% (Tables 2 and 3) is of particular interest. 0.3–0.5% of olefins were found in the products. In order to elucidate more fully the role of HBG, the study of the catalyst activity in processing of straight-run gasoline in the absence of hydrogen was carried out. It was shown that the yield of С4–С9 isoalkanes at 350 °С is 62.6%, and with the rise of temperature up to 400 °С the content of isoalkanes in the product mixture falls to 39.0%. At the same time, there is a disproportionation reaction, which leads to C10–C14 isoalkanes and C10–C13 n- alkanes appearance. Their yields are maximal at 350 °C (14.3% and 4.0% respectively). The most important is the formation of high-octane aromatic hydrocarbons – 5.4% (350 °C) and olefins (6.7%). 4. Conclusions Thus, in the absence of hydrogen the yield of C4–C9 isoal- kanes is 62.6%, and heavier isoalkanes, aromatic hydro- carbons and olefins appear. Hydrocracking to C1–C3– hydrocarbons increases at high temperatures (380– 400 °C). At 350 °C the yield of the liquid phase, i.e. gaso- line with a sufficiently high octane number is close to 100%. The analysis of the particle size of metals included in the catalyst shows that their dispersion varies within a wide range, from 20 to 200 Å. Fine particles (≤50 Å) can localize in zeolite cavities and pores of aluminum oxide, and large ones-on their outer surface. When the catalyst contacts with n-alkanes, the whole surface participates in the process, but formation of branched isomers of C6+ alkanes is possible only on the outer surface, whereas C1– C4 hydrocarbons of different structure probably appear in zeolite cavities during cracking transformation of n- alkanes capable of diffusing deep into the matrix struc- ture. Diffusion of molecules and their transformation in- crease with temperature, which is confirmed by the in- crease in cracking of n-alkanes. Supplementary materials No supplementary materials are available. Funding This research had no external funding. Acknowledgments None. Conflict of interest The authors declare no conflict of interest. Author contributions Conceptualization: A.K.Z., L.K.T. Data curation: A.K.Z. Formal Analysis: L.K.T., Y.A.A. Investigation: A.K.Z., L.K.T. Methodology: R.O.O., Y.A.A. Resources: R.O.O. Supervision: Y.A.A. Validation: A.K.Z., L.K.T. Visualization: E.B.Z. 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