Chemical compositions of the synthesized supports and catalysts are given in Table 1. The data of ICP-AES analysis fit in well with theoretical calculations. Si, Al, Mo and Co contents coincide with expected values. The increase in Al2O3/ASA ratio in the support also increases its water capacity from 0.5 to 2.8 cm3/g. Such great values could be useful in the case, when solutions with high concentration of active metals are used. In our case, the water capacity values are much higher than needed.
The ASA powder itself has very poor ability for plasticization. If aqueous solution of nitric acid is added to the ASA powder, the granulated support will have bulk crushing strength (BCS) value less than 0.3 MPa, because of bad properties of the kneading paste. Addition of 30–50 wt.% aluminum hydroxide to the kneading paste results in the increase in BCS value up to 0.4 MPa. The greater amounts of PBe (more than 90 wt.%) provides strong supports with BCS values more than 1.2 MPa. Small quantities of active metals did not provide high BSC values for catalysts with less than 90 wt.% of alumina, but the catalysts with 30–50 wt.% in a granular shape are strong enough to endure storage and overloading from one container to another.
The synthesis of composite support requires studies of its phase composition. After thermal treatment at 550ºC, aluminosilicate did not transform to another phase as it was evidenced by 29Si MAS NMR spectrum of Sup-0/100 (Figure SI1). Deconvolution of the spectrum of the Sup-0/100 reveals the presence of five overlapping signals in the region from − 70 to − 110 ppm. These signals can be assigned to tetrahedrally bonded silicon atoms neighbored by a varying number of aluminum atoms, i.e. Q4(nAl) units where n = 0 ÷ 4 [27]. Determining the integral intensities of the observed signals calculates Si/Al ratio of 2.0 for the sample Sup-0/100.
27Al MAS NMR spectroscopy enables one to distinguish reliably aluminum atoms with different coordination numbers, which are present in aluminosilicate materials [27]. The Sup-0/100 support (100% ASA) contains three types of Al atoms located in AlO4, AlO5 and AlO6 units with the relative intensities of 26%, 15%, and 59%, respectively (Figure SI2). The spectrum of the Sup-100/0 sample (pure γ-Al2O3) reveals two signals corresponding to tetrahedrally and octahedrally coordinated Al atoms. The AlO4/AlO6 ratio is 0.5 (Figure SI2). 27Al MAS NMR spectrum of the Sup-50/50 sample (Figure SI2) is the superposition of the spectra of its constituents. All three types of AlOmunits (m = 4, 5, 6) are present in the spectrum. The relative content of different Al atoms is 31%, 8% and 61% for four-, five-, and six-fold coordinated aluminum, respectively.
Table 1
– Chemical composition and physical parameters of supports and catalysts
Supports
|
Catalysts
|
Al2O3/ASA ratio
|
Si, wt.%
|
Al, wt.%
|
BCS, MPa
|
Water capacity, cm3/g
|
Bulk density, g/cm3
|
Co, wt.%
|
Mo, wt.%
|
BCS, MPa
|
Bulk density, g/cm3
|
100/0
|
-
|
52.9
|
1.4
|
0.5
|
0.7
|
2.1
|
6.1
|
1.6
|
0.8
|
90/10
|
1.1
|
51.8
|
1.2
|
0.6
|
0.6
|
2.1
|
6.1
|
1.4
|
0.7
|
70/30
|
2.9
|
49.7
|
0.8
|
1.0
|
0.5
|
2.1
|
6.0
|
0.9
|
0.5
|
50/50
|
4.8
|
47.8
|
0.5
|
1.7
|
0.3
|
2.0
|
6.1
|
0.7
|
0.4
|
30/70
|
6.7
|
46.0
|
0.4
|
2.0
|
0.3
|
2.1
|
6.1
|
0.6
|
0.3
|
10/90
|
8.6
|
43.6
|
< 0.3
|
2.8
|
0.2
|
2.1
|
6.0
|
0.35
|
0.3
|
0/100
|
9.9
|
41.8
|
< 0.3
|
2.5
|
0.2
|
2.1
|
6.1
|
< 0.3
|
0.2
|
To understand the state of Al2O3, the supports were studied by XRD method (Figure SI3). The diffraction pattern of the Sup-100/0 sample corresponds to metastable low-temperature phase of γ-Al2O3 with cubic structure of spinel type (PDF#00-029-0063). Parameters of crystal lattice are a = b = c = 7.907(2) Å, the average size of CSR is D = 5.5 nm. The diffraction pattern of the Sup-0/100 sample does not contain clear maxima, because of the X-ray amorphous properties. The broaden peak at 2θ = 65.5° cannot be ascribed to poorly crystallized phase of alumina, because it is shifted to smaller angles. Diffraction patterns of the samples with different Al2O3/ASA ratio show the increased contribution of metastable γ-Al2O3 in the samples with high alumina content.
Based on the data received, it can be concluded that the supports with Si/Al ratio 90/10, 70/30, 50/50, 30/70 and 10/90 are the mixture of ASA and Al2O3 and do not include other phases.
If we have two separate phases in supports, it can be suggested that textural properties will be a superposition of the texture of individual components. Indeed, specific surface area of supports increases with the increase of ASA content in supports. It is noted that the most drastic increase is observed when ASA content growth from 0 to 50% (Fig. 1A). Further increase in the content of ASA does not lead to such strong changes. The same tendency is observed for pore volume values of supports (Table SI4).
Because catalysts contained low amounts of active metals and further testing of catalysts included only testing in the model feedstock, such high SSA values and great pore volume are more than enough for great diffusion of the feedstock molecules through pores of catalysts. However, we considered changes in pore size distribution of supports with changes of ASA content (Fig. 1B). It was not expected that gradual increase in ASA content will change in a strange manner pore size distribution. When ASA content becomes higher, the portion of pores < 50 Å and 50–100 Å becomes lower. The portion of pores with diameters > 200Å increases with amount of ASA. The changes of pores with diameters 100–200 Å has a volcanic dependence. The greatest amount of these pores is observed for the Sup-70/30 and Sup-50/50 samples.
After supporting of active metals SSA and pore volume values become lower, however textural properties change in a similar manner with ASA content as of corresponding supports.
The quick glance on the pore size distribution curves of supports and catalysts (Figure SI5) confirms wide pore size distribution for ASA containing supports. The amount of wide pores becomes greater with ASA content, but the addition of ASA also contributes to small pores (with diameters < 40 Å).
The most attractive in introduction of ASA to the support are changes in supports acidity. If we talk about isomerization and hydrogenation reactions, the most effects will be obtained for catalysts prepared from the supports of greater acidity than alumina. According to TPD-NH3 data total concentration of acid sites of parent Al2O3 sample is by 40% lower than that of the ASA powder (Table 2). Indeed, the initial Al2O3contains much lower amount of weak and medium acid sites, while the amount of strong acid sites is similar.
Table 2
– The data of NH3-TPD method
Al2O3/ASA ratio
|
Sample
|
Concentration of acid sites, µmol/g
|
Concentration of acid sites per 1 m2 of the sample
|
Weak
|
Medium
|
Strong
|
Total
|
Parent ASA
|
183
|
362
|
76
|
621
|
1.3
|
Pseudoboehmite calcined at 550ºC
|
92
|
237
|
54
|
384
|
1.7
|
100/0
|
Support
|
113
|
251
|
72
|
432
|
2.0
|
Catalyst
|
138
|
258
|
93
|
489
|
2.7
|
90/10
|
Support
|
122
|
257
|
61
|
440
|
1.6
|
Catalyst
|
154
|
276
|
81
|
505
|
2.2
|
70/30
|
Support
|
137
|
271
|
54
|
462
|
1.4
|
Catalyst
|
173
|
315
|
83
|
571
|
2.1
|
50/50
|
Support
|
160
|
280
|
47
|
488
|
1.2
|
Catalyst
|
179
|
370
|
87
|
636
|
2.0
|
30/70
|
Support
|
170
|
355
|
84
|
608
|
1.5
|
Catalyst
|
203
|
389
|
86
|
678
|
2.0
|
10/90
|
Support
|
174
|
369
|
70
|
613
|
1.4
|
Catalyst
|
225
|
383
|
74
|
682
|
1.9
|
0/100
|
Support
|
201
|
390
|
73
|
664
|
1.5
|
Catalyst
|
219
|
416
|
69
|
704
|
1.8
|
The amount of acid sites of different strength in supports is not an algebraic sum of its components multiplied by the content of each component. The concentration of weak acid sites significantly increases after peptization of supports by nitric acid. There is no clear tendency in the change of concentration of medium and strong acid sites. It was also noted that addition of 10–50% of ASA to the support led to the decrease in concentration of acid sites per m2 of a sample from 2.0 to 1.2 (Table 2). Further increase in ASA content to 100% resulted in the slight increase of this parameter to 1.5. This tendency does not handle for catalysts that show gradual decrease in acidity with ASA addition. The changes in concentration of acid sites per m2 of a support, as will be seen below, correlate with changes in hydrogenation and isomerization activities of catalysts.
The TPD-NH3 method cannot identify LAS and BAS. Then, we used IR of pyridine adsorption method to measure concentration of BAS sites (Table 3). The ASA in the supports contributes to formation of BAS. The formation of weak acid sites is observed for supports with ASA. Moreover, the increase of ASA content from 50 to 100% results in twice increase of the amount of Brønsted acid sites in supports. It is noted that total amount of BAS sites is not much higher than the amount of weak sites. Then, the contribution of medium and strong BAS is not significant. Besides, the observed gradual increase in the amount of BAS of different strength allows us to conclude that the uneven change in strong acid sites seen in TPD-NH3data is caused by strong LAS sites.
Table 3
The acidity data by IR of pyridine adsorption method
Al2O3/ASA ratio
|
Sample
|
Brønsted acid sites, µmol/g
|
Weak
|
Total
|
100/0
|
Support
|
0
|
0
|
Catalyst
|
0
|
0
|
50/50
|
Support
|
11
|
15
|
Catalyst
|
14
|
18
|
0/100
|
Support
|
21
|
25
|
Catalyst
|
25
|
29
|
The addition of ASA to the support and catalyst is expected to change interaction between active metals and a support. The XRD data of catalysts show no structural changes of the supports after supporting active metals. XRD patterns of the catalysts with 100 − 70 wt.% of alumina in the support contain additional narrow peaks with low intensity at 2θ = 20.8, 22.1, 23.4 and 26.3° (Fig. 2), which correspond to Al2(MoO4)3 phase (PDF#00-023-0764). The formation of Al2(MoO4)3 does not observed in the case of the samples with the ASA content more than 50 wt.%. Therefore, there is lowering in the interaction between active metals and a support, when ASA content in the support is more than 70%. Then, changes in oxidation state of active metals can occur.
The oxidation state and coordination numbers of Co and Mo cations were defined from absorption spectrum obtained by DRS method (Fig. 3). The energy values of adsorption bands of Co and Mo cations were related to the values of d-d transitions common for Me cations. In all cases, the spectra could be divided into the following areas: the area from 13000 to 22000–23000 cm− 1, the area at 22000–23000 cm− 1 with high intensity and the area from 11000 to 13000 cm− 1 with the lowest intensity.
It is established that intensity of the bands in the range of 11000–13000 cm− 1 grows with ASA content in the supports that is caused by the presence of trace components in the initial ASA powder. According to chemical analysis data of the supports, the ASA powder contains about 0.08 wt.% of Na and 0.05 wt.% of Fe.
Adsorption bands in the range of 13000 to 22000–23000 cm− 1 are characteristic for Co2+ cations in tetrahedral Co2 + Td and octahedral Co2 + Oh oxygen surrounding. Shifts of adsorption bands for all cations significantly depend on the strength of crystalline field, which is formed by ligands of the first and second coordination spheres. For all studied catalysts, three bands at 15800, 17200 and 18300 cm− 1 appear in this range. These bands correspond to Co2 + Td stabilized in CoAl2O4. It is caused by d-d transition of 4A2(F)–4T1(P). In this case, the spinel can be reversed by 20% and also contains Co2 + Oh cations, which appear as a low-intensity band with the position of 21000 cm− 1. The increase in the ASA content in supports results in the gradual drop of the intensity of the bands at 15800, 17200 and 18300 cm− 1 that indicates the decrease in the amount of Co2 + Td cations and formation of Co2 + Oh. In addition, adsorption bands in the range of 20000 cm− 1 appear for the samples with more than 30 wt.% of ASA in the support. It is most probably that the bands correspond to the formation of Co2 + Oh stabilized in ASA layers. It is clearly seen that there is the broadening of the maximum of the band at the position of 18000 cm− 1 and its slight shift to 19300 cm− 1 for the samples with 90% and 10% ASA in the support. Such band is common for stabilization of Co2 + Oh cations in zeolites.
In UV area of DRS spectra, there are only bands from the charge transition between metal and ligand (CTML) for metal’s cation. The CTML can appear for both Co2+ and Mo6+ cations in the range of 22000–23000 cm− 1. Since CTML for Co2 + Td and Co2 + Oh are higher than 40000 cm− 1 [28], it can be assumed that there is only CTML from Mo6+ in the range of 22000–40000 cm− 1 in studied samples. The increase in ASA content in supports results in the decrease of the intensity of CTML from Mo6+ and its shift to UV range of the spectra. Thus, there is the blue shift that can indicate the decrease in a particle size of active component precursors.
In present work, the oxide state of CoMo catalysts is a precursor of the sulfide active component. Obviously, the weakening interaction between the oxide precursor and support should alter morphology of sulfide active component particles.
The examples of HRTEM images of ASA and alumina fragments of CoMo-50/50 catalyst are shown in Figure SI6. It is noted that there are remarkable differences in location of active component particles on alumina and ASA surfaces (Table 4). CoMoS particles on alumina surface have higher stacking numbers, higher amount of slabs per surface unit and shorter paticles comparing to the ones over the ASA surface. About 40% of all CoMoS phase slabs on alumina have multilayered structure (Table 4). The ASA surface preferentially contains long monolayer particles with the average length of 2.8-3.0 nm and the average stacking number of 1.6–1.7.
Morphology of active component particles over ASA and Al2O3 constituents of supports are controversial to the literature data. It is often observed that the stacking of the crystallites is enhanced when silica is incorporated to alumina support, while particle length is similar or shorter [29, 30]. However, the data in [30] also show that promotion of W/SiO2-Al2O3 catalyst by Ni leads to the decrease in particle length and stacking of the sulfide active component. Then, we can suggest similar effect for our catalysts that the weakening interaction of active metals and support (especially detected by XRD and UV methods for Co) could result in the lowering stacking number in CoMo catalysts doped by ASA caused by improved promotion of sulfide active component.
Mo3d, Co2p, S2s, S2p, AlKLL and Si2p XPS spectra of sulfide CoMo catalysts are shown in Figure SI7. The XPS spectra of Si and Al contain the wide peak at 102.5-102.7 eV, which corresponds to Si in oxygen surrounding. Different Si and O bonding and possible formation of Si-O-Al bonds account for great width of the peak. It is consistent with NMR 29Si data. Decreasing ASA content results in the decrease in the intensity of the peak.
Mo3d spectra show that the ASA content in supports has a significant impact on Mo state. The peak at 228.9 eV is characteristic for Mo4+ ions in sulfur surrounding (Figure SI7) in the composition of CoMoS phase [13, 31, 32]. Deconvolution of the peak to individual components shows the presence of Mo in the form of Mo5+ and Mo6+ (Figure SI8). Concentrations of various molybdenum states in sulfide catalysts are given in Table 5. There is the gradual reduction of Mo4+ content and the increase of Mo5+ with increasing ASA content in supports, while portion of Mo6+is similar (8–10%). It was noted that the Mo/S ratio on the surface increased, when more than 30% of ASA was added to the support.
Table 4
The HRTEM data for CoMo sulfide catalysts
Sample
|
Location of active component
|
Average slabs number per 1000 nm2
|
Average stacking number
|
Average slab length, nm
|
Portion of active component particles with different stacking numbers,%
|
1 layer
|
2 layers
|
3 layers
|
4 + layers
|
CoMo-100/0
|
Al2O3
|
33
|
2.2
|
2.2
|
35
|
30
|
25
|
10
|
ASA
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
CoMo-90/10
|
Al2O3
|
27
|
2.3
|
2.3
|
27
|
33
|
29
|
11
|
ASA
|
12
|
1.6
|
2.8
|
54
|
31
|
12
|
3
|
CoMo-70/30
|
Al2O3
|
26
|
2.3
|
2.3
|
25
|
35
|
30
|
10
|
ASA
|
13
|
1.6
|
2.9
|
54
|
32
|
11
|
3
|
CoMo-50/50
|
Al2O3
|
25
|
2.3
|
2.4
|
22
|
34
|
33
|
11
|
ASA
|
14
|
1.7
|
2.8
|
50
|
33
|
14
|
3
|
CoMo-30/70
|
Al2O3
|
26
|
2.3
|
2.3
|
24
|
37
|
29
|
10
|
ASA
|
14
|
1.7
|
2.9
|
49
|
35
|
12
|
4
|
CoMo-10/90
|
Al2O3
|
27
|
2.4
|
2.3
|
24
|
38
|
28
|
10
|
ASA
|
13
|
1.6
|
3
|
52
|
33
|
12
|
3
|
CoMo-0/100
|
Al2O3
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
ASA
|
19
|
1.7
|
3
|
48
|
34
|
15
|
3
|
Co2p spectra of the catalysts contain the peak with the binding energy 779.0 eV. It corresponds to cobalt II in sulfur-oxygen surrounding [33]. The presence of the peak at 162.0 ± 0.2 eV, which is common for S2- ions, and the peak at 779.0 eV in Co2p spectra indicates the formation of CoMoS phase in sulfide catalysts [34, 35]. It was not possible to make deconvolution of Co2p spectra because of its low intensity and high noise level. However, it was possible to estimate Co/Mo surface ratio from peaks intensities. The data shows the increase in Co/Mo ratio for catalysts doped with ASA. The higher ASA content, the higher Co/Mo ratio. These data confirm the previous assumption on the improvement of promotion of MoS2 slabs.
Catalytic activity of the catalysts was estimated in two reactions: hydrodesulfurization of thiophene and conversion of 1-hexene. The Fig. 4 depicts thiophene conversion obtained at 220 and 240ºC. The introduction of ASA leads to the decrease in thiophene conversion from 58 to 50% at 220ºC and from 80 to 68% at 240ºC. The decrease in hydrodesulfurization activity correlates with the decrease in the amount of Mo4+ state in the XPS data and the increase in Co/Mo surface ratio. Then, it can be concluded that this reaction route is completely driven by CoMoS phase.
Table 5
– XPS data of sulfide CoMo/ASA + Al2O3 catalysts
Al2O3/ASA ratio
|
100/0
|
90/10
|
70/30
|
50/50
|
30/70
|
10/90
|
0/100
|
Mo4+, %
|
82.8
|
75.9
|
73.4
|
71.3
|
69.5
|
68.9
|
66.8
|
Mo5+, %
|
11.5
|
14.1
|
16.8
|
19.7
|
22.9
|
23.2
|
24.3
|
Mo6+, %
|
5.7
|
10.0
|
9.3
|
9.0
|
7.7
|
7.9
|
8.9
|
Co/Mo
|
0.38
|
0.36
|
0.35
|
0.40
|
0.46
|
0.49
|
0.44
|
Co/S
|
0.11
|
0.09
|
0.09
|
0.11
|
0.13
|
0.14
|
0.13
|
Mo/S
|
0.30
|
0.28
|
0.35
|
0.45
|
0.4
|
0.44
|
0.37
|
BE S2p – 162.2 eV
|
BE Mo3d − 228.9 eV
|
BE Co2p – 779.0 eV
|
Location of CoMoS phase is also important for hydrodesulfurization activity. Comparison of active component morphology for ASA and Al2O3 constituents allows us to conclude that the amount of ASA does not influence visibility, slab length and stacking number of active component particles. Then, dispersion of active metals is similar for catalysts. If we increase the amount of ASA in the catalyst and do not observed changes in visibility, we can suggest that catalysts with greater amount of ASA contain more monolayered slabs on ASA and slabs on ASA, which locate parallel to the support surface. It is likely such coordination of active component slabs on ASA is less preferable for hydrodesulfurization reaction of thiophene.
The presence of 1-hexene in the model mixture allows estimation of hydrogenation and hydroisomerizaton activities of catalysts. It is known that 1-hexene transforms to n-hexane, (Z)-3-hexene, (E)-2-hexene, (E)-3-hexene and (Z)-2-hexene under testing conditions. The amount of branched isomers was less than 0.05 wt%. Conversion of 1-hexene becomes slightly lower, when ASA is introduced to the support. The remarkable effects were observed for the HYD1 − hexene parameter, which includes conversion of 1-hexene to other isomers. The greatest decrease of the HYD1 − hexene value is detected for the catalysts with more than 50% of ASA in the support. When ASA content achieves 50% in the support, the HYD1 − hexene value drops by 3 times.
Such changes in HYD1 − hexene value are caused by the improvement in isomerization activity (ISO) of catalysts. The Fig. 5 depicts isomerizing activity of catalysts at 220 and 240ºC. The drastic change in isomerizing activity is detected for CoMo-50/50 catalyst, especially at 240ºC. Further increase in ASA content in supports does not lead to significant improvement in ISO activity.
If we talk about hydrotreatment of the hydrocarbon mixture that simulates FCC gasoline, it is necessary to take into attention octane numbers of the products of 1-hexene conversion, because it is the most important contributor to octane number of the feedstock. Research octane number of hexene-1 is 76.4, while the products of its conversion have the following RONs: n-hexane – 24.8, 3-hexene – 94.0, 2-hexene – 92.7. Therefore, the isomerizing products have much higher octane numbers than the initial 1-hexene. We can expect the increase in the RON number of the hydrotreated product for the case, when the amount of formed isomers will be significant.
RON values of the initial feedstock and hydrotreated products were calculated as the sum of the RON values of the components, every of which is multiplied by the weight of the component in liquid and gas samples (Eq. 5). The RON values of the components were taken from the data in [26]. The resulting data are given in Fig. 6. The allowed value of the RON loss after hydrotreatment in industry is about 1.5 point. This area is shown as shaded in the chart. The RON number of the hydrotreated product grows with ASA content in the support. The significant increase in RON value is observed for the catalyst with 50% of ASA. It was noted that the isomerizing activity of catalysts with more than 50% of ASA were less sensitive to the increase in the process temperature. The resulting octane number of hydrotreated product was in the range of the allowed values.
The RON values are proportional to the acidity of supports and catalysts and inversely proportional to concentration of acid sites per 1 m2 of the surface. The RON values especially depends on the amount of medium and weak acid sites. As it was mentioned above, the strong increase in the content of medium acid sites was caused by LAS contribution. The increase of weak acid sites can be caused by both LAS and BAS sites.
The increase in the amount of BASs in studied catalysts can facilitate protonating reactions of converted molecules. Weak BASs mostly presented in the ASA powder and ASA-containing supports contribute to isomerization reactions, while alkylation and cracking reactions preferentially occur with medium and strong BASs [36]. In present work, introduction of ASA to support influences migration of the double bond of 1-hexene followed by preferential formation of (Z)-3-hexene, (E)-3-hexene and 2-hexenes. Migration of double bond can be implemented by both BASs of supports and CoMoS phase sites.
When BAS is located nearby sulfide active component particle, an olefin is first protonated over BAS followed by conversion at coordinately unsaturated site (CUS) of CoMoS phase. In this case, isomerization reactions are more energetically profitable than removal of sulfur or hydrogenation [2, 36]. It can explain the considerable changes in HYD and ISO activities for the samples with more than 50 wt. % of ASA (Fig. 7) due to the formation of weak and medium BAS in catalysts. Introduction of ASA to CoMo/Al2O3 catalysts results in the increase of weak and medium LASs, which could increase catalyst’s activity in HDS of sulfur compounds [37]. Weak LASs also contribute to hydrogenation of unsaturated bonds as well as HDS of sulfur molecules due to activation of hydrogen. Small amounts of strong LASs in studied samples can be respective for the increased interaction between active component and support [38–41] that has a negative influence on HDS activity.
It is interesting that some kind of a breaking point in hydrodesulfurization, hydrogenating and isomerizing activities is observed for the catalysts with 50 wt.% of ASA (Fig. 7). This sample demonstrates high isomerizing/low hydrogenating activity along with insignificant drop of hydrodesulfurization activity. The explanation of such phenomenon is in combination of the properties of active component and the support (Fig. 8). On the one hand, the CoMo-50/50 catalyst has lower amount of sulfide active phase comparing to the catalyst without ASA. However, it is characterized by higher promotion degree of the active phase than CoMo-100/0 and do not contain Co that was separated from the CoMoS phase and interacted with the support. Therefore, the drop in hydrodesulfurization activity is not as drastic as it could be. On the hydrogenating/isomerizing point of view, the presence of the active phase along with the increase in the ASA content in the support will result in in blocking active sites that are responsible for isomerization and hydrogenation. However, the fact is that the enhancement in the amount of isomerization active sites is more significant, than of hydrogenating ones, due to the addition of 50% ASA.
Why do we point out the CoMo-50/50 catalyst instead of other catalysts with ASA content higher than 50%? The reason is that the addition of more than 50% ASA to the catalyst does not lead to considerable changes in hydrodesulfurization and hydrogenation properties, especially at high temperatures, while its performance characteristics, such as mechanical strength, become worse. The difference in mechanical strength between catalysts with 50, 70 and 90% of ASA is not very big, but the choice should be done to the catalyst with the highest value of the characteristic. The increase in the mechanical strength can be achieved by changes the properties of the boehmite, but these results will be shown in the following paper. It is known that the strength properties of the support and the catalyst significantly influenced by the morphology of alumina particles [42]. However, this topic will be covered in the next work.