Direct Hydrogen Production from Extra-Heavy Crude Oil under Supercritical Water Conditions Using a Catalytic (Ni-Co/Al 2 O 3 ) Upgrading Process

: The generation of hydrogen from unconventional oil is expected to increase signiﬁcantly during the next decade. It is commonly known that hydrogen is an environmentally friendly alternative fuel, and its production would partially cover the gap in energy market requirements. However, developing new cheap catalysts for its production from crude oil is still a challenging area in the ﬁeld of petroleum and the petrochemical industry. This study presents a new approach to synthesizing and applying promising catalysts based on Ni, Co, and Ni-Co alloys that are supported by aluminum oxide Al 2 O 3 in the production of hydrogen from extra-heavy crude oil in the Tahe Oil Field (China), in the presence of supercritical water (SCW). The obtained catalysts were characterized via scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, transmission electron microscopy (TEM), and, X-ray diffraction analysis (XRD). The obtained XRD data showed 3.22% of Co 2+ in the Co/Al 2 O 4 catalyst, 10.89% of Ni 2+ in the Ni/Al 2 O 4 catalyst, and 1.51% of Co 2+ and 2.42% of Ni 2+ in the Ni-CoAl 2 O 3 bimetallic catalyst. The BET measurements of the obtained catalysts showed a surface area ranging from 3.04 to 162 m 2 /g, an average particle size ranging from 0.037 to 0.944 µ m, and micropore volumes ranging from 0.000377 to 0.004882 cm 3 /g. The thermal, SCW, and catalytic upgrading processes of the studied samples were conducted in a discontinuous autoclave reactor for 2 h at a temperature of 420 ◦ C. The obtained results revealed that thermal upgrading yielded 1.059 mol.% of H 2 , and SCW led to 6.132 mol.% of H 2 ; meanwhile, the presence of Ni-CoAl 2 O 3 provided the maximal rate of hydrogen generation with 11.783 mol.%. Moreover, Ni-CoAl 2 O 3 and NiAl 2 O 3 catalysts have been found to possess good afﬁnity and selectivity toward H 2 (11.783 mol.%) and methane CH 4 (40.541 mol.%). According to our results, the presence of SCW increases the yield of upgraded oil (from 34.68 wt.% to 58.83 wt.%) while decreasing the amount of coke (from 51.02 wt.% to 33.64 wt.%) due to the signiﬁcant amount of hydrogen generation in the reaction zone, which reduces free-radical recombination, and thus, improves oil recovery. Moreover, the combination of SCW and the synthetized catalysts resulted in a signiﬁcant decrease in asphaltene content in the upgraded oil, from 28% to 2%, as a result of the good redistribution of hydrogen over carbons (H/C) during the upgrading processes, where it increased from 1.39 to 1.41 in the presence of SCW and reached 1.63 in the presence of the Ni-CoAl 2 O 3 catalyst. According to the XRD results of the transformed form of catalysts (CoNi 3 S 4 ), after thermal processing, heteroatom removal from extra-heavy crude oil via oxidative and adsorptive desulfurization processes is promoted. These ﬁndings contribute to the expanding body of knowledge on hydrogen production from in situ unconventional oil upgrading.


Introduction
According to the global energy outlook, energy demand will continue to rise and may reach approximately 53% by 2030 [1].However, according to the EIA, by 2050, hydrogen generation will account for 10% of total final energy consumption [2].The future of hydrogen fuel generation will not only partially compensate for energy demand, but will also allow us to combat the environmental impact of greenhouse emissions [3].Although hydrogen generation is intriguing, there is still a lack of interest in creating efficient and acceptable strategies to increase its production and processing from unconventional oil, biomass, or water [4].It is well known that hydrogen may be created through several petrochemical processes such as hydrocarbon reforming, steam reforming, and partial oxidation [5].The hydrocarbon reforming process is one of the oldest processes for producing hydrogen.It is an endothermic process that requires an external heat source and may create monoxide and dioxide carbon with a 3:1 hydrogen to monoxide carbon (H 2 /CO) ratio.Furthermore, this procedure is commonly applied on an industrial scale and is carried out in a variety of reactors with high and low temperatures.In other words, high-temperature hydrogen production requires temperatures greater than 350 • C in the presence of ironbased catalysts.In the presence of copper-based catalysts, low-temperature generation needs temperatures ranging from 210 to 330 • C [6,7].For most common hydrocarbons, steam reforming is a fuel refining process that needs temperatures ranging from 180 • C to more than 500 • C. It is commonly regarded as one of the most effective techniques for producing hydrogen at higher heating values, with an efficiency of more than 80-85% when methane is used as feedstock.[8,9].
A significant portion of the scientific community considers partial oxidation (PO) and catalytic partial oxidation (CPO) of hydrocarbons as promising strategies for commercial hydrogen generation, such as automobile fuel cells and other uses.Non-catalytic partial oxidation of hydrocarbons in the presence of oxygen is normally carried out at flame temperatures ranging from 1300 to 1500 • C to achieve full conversion and carbon reduction [5,10].Biomasses are thought to be the most plausible renewable organic alternative for petroleum [11,12].The creation of hydrogen from the aforementioned sources relies on several methods such as gasification, pyrolysis, and conversion to liquid fuels via supercritical extraction, liquefaction, hydrolysis, and so on.Biomass and coal gasification rely heavily on partial oxidation of these materials to produce gaseous products (H 2 , CH 4 , CO, CO 2 , and N 2 ) [13].As a result, adding steam and/or oxygen to the gasification process would result in steam reforming and a syngas stream with a 2:1 H 2 /CO ratio [10,14].Additionally, it was discovered that superheated steam (800-1000 • C) may be utilized to reform dry biomass, resulting in large hydrogen yields [14].
Downstream hydrogen generation from the aforementioned approaches has always been the subject of research.Despite this interest, no one has researched the in situ generation of hydrogen through improved oil recovery technologies during the production of unconventional oil resources in the presence of SCW and nickel-and cobalt-based catalysts, to the best of our knowledge.As a result, the focus of this research will be on the hydrothermal upgrading of unconventional oil sources in supercritical water using bimetallic catalysts for hydrogen generation.
A growing number of studies have discovered that supercritical water (SCW) plays an important role in hydrogen production during in situ upgrading processes due to its ability to dissolve in organic matter, as well as its coolant properties and the excellent "cage effect," which prevents coke formation earlier during thermally enhanced heavy oil recovery [15][16][17].Unconventional oil in situ or ex situ upgrading methods in the presence of supercritical water (SCW) can be regarded as effective and acceptable ways for producing not only oil, but also hydrogen, which is expected to play an important part in energy demand soon.SCW is a thermodynamic state of water that exists above its critical conditions (374.3 • C and 22.1 MPa) [18,19].SCW is also a homogeneous phase in which the phase of the gas-liquid interface vanishes and most hydrogen bonds weaken, affecting diffusion and the dissolving ability [20,21].
The ability of the SCW to behave as a gas and a liquid during heavy oil thermal upgrading processes in the presence of transition metals acting as effective catalysts during cracking and aquathermolysis reactions would effectively intensify synergistically heavy oil upgrading and stimulate dehydrogenation of its components, resulting in a significant additional release of hydrogen.It is also worth noting that employing metal oxides (catalysts) in the upgrading process of extra-heavy oils or petroleum residues from oil refineries or petrochemical industries is regarded as one of the most promising approaches for the ex situ upgrading of heavy hydrocarbons.This approach has the potential to enhance heavy oil transport and treatment operations [22][23][24][25][26].
The use of transition metal-based nanoparticles with single, double, or multiple alloys is now widely regarded as one of the most advanced ways for improving heavy oil and residue upgrading processes [27,28].Because of their smaller sizes, increased surface area, better dispersity, and catalytic activity, as well as their thermal stability, nanomaterial-based catalysts work well during heavy oil cracking reactions and avoid coke formation earlier.One of the primary benefits of employing nanoparticles is their ease of recycling, which makes them suitable for new catalytic systems in hydrothermal upgrading processes [29][30][31][32][33][34][35].
Mohammed et al. [36] investigated the process of heavy oil upgrading in the presence of supercritical water and a ZrO 2 -Al 2 O 3 -FeO x catalyst in a batch reactor.The authors discovered that hematite converts to magnetite more significantly than magnetite evolves to hematite.It was discovered that the obtained hydrogen from the upgrading process was roughly 8%.However, the extra hydrocarbons depleted the lattice oxygen, causing the catalyst to deactivate.Duan et al. [37] also performed experimental research on the hydrothermal upgrading of crude algal bio-oil in the presence of supercritical water and a Pt/C catalyst.It has been discovered that the presence of Pt/C increases the removal of heteroatoms (O, N, and S) from improved oil.Furthermore, the mobility of the produced oil increased as a result of viscosity reduction.In addition, this study reported about 5.8 wt.% of H 2 production in the composition of the released gases.Recent works conducted by Remón et al. [38] about the SCW effect on bio-oil upgrading processes in the presence of Ni-Co catalysts supported by carbon nanofibers proved that the use of Ni-Co/CNFs in SCW conditions drastically enhances the properties of the original feedstock and yields higher amounts of H 2 production (18.0%).Under similar conditions, Xiaojuan et al. [39] used Ni-CoAl 2 O 3 for the methane steam reforming process.It was suggested that the Ni-CoAl 2 O 3 catalyst plays a crucial role in hydrogen production from methane.Despite the considerable effect generated by different transition metals such as Ni-Co, Ni-Mo, and NiW mixtures on various types of feedstock upgrading processes [40][41][42][43], until recently, nobody has ever utilized Ni/Al 2 O 4 , Co/Al 2 O 4 , and Ni-CoAl 2 O 3 for hydrogen production from extra-heavy oil upgrading processes.Until now, catalysts have been utilized to produce hydrogen ex situ in petrochemical and refining operations.In light of recent technological advancements in the field of EOR, there is now much concern about the in situ production of hydrogen from heavy and extra-heavy oil in situ upgrading processes.This paper investigates how to stimulate heavy oil upgrading processes by using Ni/Al 2 O 4 , Co/Al 2 O 4, and Ni-CoAl 2 O 3 catalysts in the presence of SCW.Our understanding of hydrogen generation from extraheavy oil in situ upgrading procedures is based on a small amount of data.As a result, we used scanning electron microscopy (SEM), transmission electron microscopy (TEM) equipped with energy dispersive X-ray (EDX), and parametric approaches to investigate the influence of several transition metal-based catalysts on heavy oil thermal upgrading under SCW circumstances.Furthermore, the hydrogen (H 2 ) production was assessed using GC chromatographic methods, whereas the composition and attributes of the examined extra-heavy crude oil and upgraded oil were measured through SARA analysis, chemical elements (CHSN/O), gas chromatography (GC), and GC-MS.The observed results, in our opinion, provide critical evidence of the potential production of hydrogen through unconventional oil in situ hydrothermal upgrading in the presence of SCW and transition metal-based catalysts.

Hydrothermal Catalytic Effect on Gaseous Production in the Presence of Catalysts
The thermal upgrading process of extra-heavy oil in the absence of SCW did not show a significant impact on the production of hydrogen, which has been found to equal to only 1.05 mol.%.However, hydrothermal upgrading in the presence of SCW has increased the hydrogen production yield to 6.13 mol.%.Moreover, hydrothermal upgrading in the presence of SCW and the Ni-CoAl 2 O 3 catalyst revealed an even higher yield of hydrogen production (11.78 mol.%), as shown in Figures 1 and 2. Interestingly, for the hydrothermal experiments of samples S-3, S-4, and S-5 in the presence of SCW and catalysts, the methane (C 1 ) yield has been found to increase from 9.94 mol.% for the S-1 to reach a maximum of 40.54 mol.% in the presence of Ni/Al 2 O 4 .Obviously, the released rate of methane has been found to decrease in the presence of the Ni-CoAl 2 O 3 catalyst.This could be related to methane consumption from steam reforming, which produces hydrogen; consequently, the yield of H 2 would increase more in the S-5 sample.On the other side, the organic gases C 2 -C 4 also were found to decrease from sample S-3, which explains how the use of nickel and cobalt catalysts can inhibit the cracking process of C-C bonds.In addition, hydrogen sulfur gas (H 2 S) was not detected in the composition of the investigated gases, and the reason can be attributed to the low content of sulfur in the crude oil, as reported in previous works [44,45].The obtained results point toward an increased trend in carbon dioxide formation of the CO 2 yield during the heavy oil upgrading process in the presence of SCW and catalysts with a maximum yield of 2.20 mol.% in S-4.Thus, the trend of the CO 2 yield depending on the conditions allows us to conclude that the SCW and catalysts are two key factors for initiation of the water-gas shift reaction.Typically, steam reforming is one of the most important approaches for hydrogen production from methane, which requires a high ratio of H 2 O/CH 4 [46].As can be seen from Figure 1, methane has been significantly consumed to generate hydrogen through steam reforming during extra-heavy oil catalytic upgrading in the presence of 2 mol.% of Ni-CoAl 2 O 3 .Consequently, the ratio of H 2 /CO reaches a maximum value of 3.68 compared to other samples, which revealed a lower H 2 /CO ratio (<2) such as in S-1 (H 2 /CO = 1.43),S-2 (H 2 /CO = 1.19),S-3 (H 2 /CO = 1.90), and S-4 (H 2 /CO = 1.65).In their work, Preeti et al. [47] found a higher ratio of synthetic gas (H 2 /CO = 3) during steam reforming of methane, whereas the ratio required for the Fischer-Tropsch process or methanol synthesis was found equal to H 2 /CO = 2 [48,49].
production of hydrogen through unconventional oil in situ hydrothermal upgrading in the presence of SCW and transition metal-based catalysts.

Hydrothermal Catalytic Effect on Gaseous Production in the Presence of Catalysts
The thermal upgrading process of extra-heavy oil in the absence of SCW did not show a significant impact on the production of hydrogen, which has been found to equal to only 1.05 mol.%.However, hydrothermal upgrading in the presence of SCW has increased the hydrogen production yield to 6.13 mol.%.Moreover, hydrothermal upgrading in the presence of SCW and the Ni-CoAl2O3 catalyst revealed an even higher yield of hydrogen production (11.78 mol.%), as shown in Figures 1 and 2. Interestingly, for the hydrothermal experiments of samples S-3, S-4, and S-5 in the presence of SCW and catalysts, the methane (C1) yield has been found to increase from 9.94 mol.% for the S-1 to reach a maximum of 40.54 mol.% in the presence of Ni/Al2O4.Obviously, the released rate of methane has been found to decrease in the presence of the Ni-CoAl2O3 catalyst.This could be related to methane consumption from steam reforming, which produces hydrogen; consequently, the yield of H2 would increase more in the S-5 sample.On the other side, the organic gases C2-C4 also were found to decrease from sample S-3, which explains how the use of nickel and cobalt catalysts can inhibit the cracking process of C-C bonds.In addition, hydrogen sulfur gas (H2S) was not detected in the composition of the investigated gases, and the reason can be attributed to the low content of sulfur in the crude oil, as reported in previous works [44,45].The obtained results point toward an increased trend in carbon dioxide formation of the CO2 yield during the heavy oil upgrading process in the presence of SCW and catalysts with a maximum yield of 2.20 mol.% in S-4.Thus, the trend of the CO2 yield depending on the conditions allows us to conclude that the SCW and catalysts are two key factors for initiation of the water-gas shift reaction.Typically, steam reforming is one of the most important approaches for hydrogen production from methane, which requires a high ratio of H2O/CH4 [46].As can be seen from Figure 1, methane has been significantly consumed to generate hydrogen through steam reforming during extra-heavy oil catalytic upgrading in the presence of 2 mol.% of Ni-CoAl2O3.Consequently, the ratio of H2/CO reaches a maximum value of 3.68 compared to other samples, which revealed a lower H2/CO ratio (<2) such as in S-1 (H2/CO = 1.43),S-2 (H2/CO = 1.19),S-3 (H2/CO = 1.90), and S-4 (H2/CO = 1.65).In their work, Preeti et al. [47] found a higher ratio of synthetic gas (H2/CO = 3) during steam reforming of methane, whereas the ratio required for the Fischer-Tropsch process or methanol synthesis was found equal to H2/CO = 2 [48,49].

Product Conversion and Distribution in the Upgraded Products
The effect of the opted catalysts and SCW on the extra-heavy oil upgrading process and product distribution is presented in Figure 3.The obtained results revealed that the thermal upgrading of extra-heavy oil without SCW and catalysts is highly characterized by thermal decomposition and a fast recombination reaction of free radicals, which led to a high coke formation (around 51.02 wt.%) and a considerable amount of gases (14.30wt.%).After 2 h of thermal upgrading, the yield of the upgraded oil reached 34.68 wt.% which is, relatively, considered a low value (see sample S-1 in Figure 3).Yet, the presence of SCW has changed the reaction pathway completely by decreasing the condensation rate of resins and asphaltenes.Furthermore, the obtained results confirmed the crucial role played by SCW in the extra-heavy oil upgrading process, where its presence led to an increase in the yield of the upgraded oil from 34.68 wt.% to 58.83 wt.% and a decrease in the amount of the obtained coke from 51.02 wt.% to 33.64 wt.%.Our findings would seem to suggest that the presence of SCW in S-2 plays an important role in delaying the recombination of the cracked free radicals because it can be, at certain conditions, a source of hydrogen production and a high dispersive agent in the reaction medium.In addition, it can overcome the barrier of mass transfer, which leads, therefore, to decreasing slightly the yield of the released gases from 14.30 wt.% to 7.53 wt.% because of the associated cage effect.The decrease in the released gas yield and the increase in the upgraded oil yield would seem to prove the efficient contribution of SCW in the hydrothermal upgrading reaction because of its dispersive properties (the cage effect), which prevent the early recombination of heavy free radicals [50].The most striking result to emerge from the obtained data is that using supported catalysts of Ni, Co, and Ni-Co on aluminum oxide could significantly improve the performance of the heavy oil hydrothermal upgrading process (S-3, S-3, and S-3, respectively).The results of heavy oil catalytic upgrading showed that the use of the Co/Al2O4 catalyst slightly increased the total yield of released gases from 5.64 wt.% to 8.01 wt.%, whereas the coke formation decreased to 23.97 wt.%.However, the upgraded oil yield was increased to 65.34 wt.%.Besides, a similar effect has been generated from the application of the Ni/Al2O4 catalyst in terms of increasing the yield of the upgraded oil, except for a slight increase in released gas content and an insignificant decrease in coke formation.This slight increase in gas yield in the presence of CoAl2O4 and Ni/Al2O4 catalysts is not only related to the high effect of Co and Ni on dehydrogenation reactions and the important role played by Al2O3 in the cleavage of C-C bonds, but it is related as well to the yields of C1, H2, and CO2 increasing, which is in complete consistency with the results of Hart Abasari et al. [51].The obtained results suggest that combining both metals, Ni-CoAl2O3, results in a 11.783 mol.% hydrogen yield and a maximum of 72.26 mol.% of upgraded oil.In addition, this combination led to a significant decrease in coke and gas yield.

Product Conversion and Distribution in the Upgraded Products
The effect of the opted catalysts and SCW on the extra-heavy oil upgrading process and product distribution is presented in Figure 3.The obtained results revealed that the thermal upgrading of extra-heavy oil without SCW and catalysts is highly characterized by thermal decomposition and a fast recombination reaction of free radicals, which led to a high coke formation (around 51.02 wt.%) and a considerable amount of gases (14.30wt.%).After 2 h of thermal upgrading, the yield of the upgraded oil reached 34.68 wt.% which is, relatively, considered a low value (see sample S-1 in Figure 3).Yet, the presence of SCW has changed the reaction pathway completely by decreasing the condensation rate of resins and asphaltenes.Furthermore, the obtained results confirmed the crucial role played by SCW in the extra-heavy oil upgrading process, where its presence led to an increase in the yield of the upgraded oil from 34.68 wt.% to 58.83 wt.% and a decrease in the amount of the obtained coke from 51.02 wt.% to 33.64 wt.%.Our findings would seem to suggest that the presence of SCW in S-2 plays an important role in delaying the recombination of the cracked free radicals because it can be, at certain conditions, a source of hydrogen production and a high dispersive agent in the reaction medium.In addition, it can overcome the barrier of mass transfer, which leads, therefore, to decreasing slightly the yield of the released gases from 14.30 wt.% to 7.53 wt.% because of the associated cage effect.The decrease in the released gas yield and the increase in the upgraded oil yield would seem to prove the efficient contribution of SCW in the hydrothermal upgrading reaction because of its dispersive properties (the cage effect), which prevent the early recombination of heavy free radicals [50].The most striking result to emerge from the obtained data is that using supported catalysts of Ni, Co, and Ni-Co on aluminum oxide could significantly improve the performance of the heavy oil hydrothermal upgrading process (S-3, S-3, and S-3, respectively).The results of heavy oil catalytic upgrading showed that the use of the Co/Al 2 O 4 catalyst slightly increased the total yield of released gases from 5.64 wt.% to 8.01 wt.%, whereas the coke formation decreased to 23.97 wt.%.However, the upgraded oil yield was increased to 65.34 wt.%.Besides, a similar effect has been generated from the application of the Ni/Al 2 O 4 catalyst in terms of increasing the yield of the upgraded oil, except for a slight increase in released gas content and an insignificant decrease in coke formation.This slight increase in gas yield in the presence of CoAl 2 O 4 and Ni/Al 2 O 4 catalysts is not only related to the high effect of Co and Ni on dehydrogenation reactions and the important role played by Al 2 O 3 in the cleavage of C-C bonds, but it is related as well to the yields of C 1 , H 2, and CO 2 increasing, which is in complete consistency with the results of Hart Abasari et al. [51].The obtained results suggest that combining both metals, Ni-CoAl 2 O 3 , results in a 11.783 mol.% hydrogen yield and a maximum of 72.26 mol.% of upgraded oil.In addition, this combination led to a significant decrease in coke and gas yield.

SARA Analysis of Initial and Upgraded Oil
The results of the SARA fraction analysis of the initial and upgraded oils are presented in Figure 4.The obtained data revealed that high-molecular-weight molecules break down into light fractions for both catalytic and non-catalytic extra-heavy oil upgrading processes in the presence and absence of SCW.

Saturate fractions
The thermal and hydrothermal decomposition of extra-heavy oil in the absence and presence of SCW, and Ni-and Co-based catalysts, showed relatively different impacts on the saturate fractions.As shown in Figure 4, the amount of saturates in the non-catalytic upgraded oil without SCW reached 66 wt.%.This increase in the content of the saturate fraction can be related to the thermal cracking of aromatic, resin, and asphaltene fractions via the cleavage of C-C, C-H, and C heteroatom (S, N, and O) bonds.Another reason would be the dealkylation of alkyl aromatic compounds, as well as of the alkylation reaction of some fragments of saturated molecules.Therefore, the content of aromatics decreased from 21% to 9%, resins from 22% to 3%, and asphaltenes from 28% to 23%.The comparison between heavy oil thermal processing and catalytic thermal processing in the presence of SCW and catalysts showed a different mechanism of the upgrading process.

SARA Analysis of Initial and Upgraded Oil
The results of the SARA fraction analysis of the initial and upgraded oils are presented in Figure 4.The obtained data revealed that high-molecular-weight molecules break down into light fractions for both catalytic and non-catalytic extra-heavy oil upgrading processes in the presence and absence of SCW.

SARA Analysis of Initial and Upgraded Oil
The results of the SARA fraction analysis of the initial and upgraded oils are presented in Figure 4.The obtained data revealed that high-molecular-weight molecules break down into light fractions for both catalytic and non-catalytic extra-heavy oil upgrading processes in the presence and absence of SCW.

Saturate fractions
The thermal and hydrothermal decomposition of extra-heavy oil in the absence and presence of SCW, and Ni-and Co-based catalysts, showed relatively different impacts on the saturate fractions.As shown in Figure 4, the amount of saturates in the non-catalytic upgraded oil without SCW reached 66 wt.%.This increase in the content of the saturate fraction can be related to the thermal cracking of aromatic, resin, and asphaltene fractions via the cleavage of C-C, C-H, and C heteroatom (S, N, and O) bonds.Another reason would be the dealkylation of alkyl aromatic compounds, as well as of the alkylation reaction of some fragments of saturated molecules.Therefore, the content of aromatics decreased from 21% to 9%, resins from 22% to 3%, and asphaltenes from 28% to 23%.The comparison between heavy oil thermal processing and catalytic thermal processing in the presence of SCW and catalysts showed a different mechanism of the upgrading process.

Saturate Fractions
The thermal and hydrothermal decomposition of extra-heavy oil in the absence and presence of SCW, and Ni-and Co-based catalysts, showed relatively different impacts on the saturate fractions.As shown in Figure 4, the amount of saturates in the non-catalytic upgraded oil without SCW reached 66 wt.%.This increase in the content of the saturate fraction can be related to the thermal cracking of aromatic, resin, and asphaltene fractions via the cleavage of C-C, C-H, and C heteroatom (S, N, and O) bonds.Another reason would be the dealkylation of alkyl aromatic compounds, as well as of the alkylation reaction of some fragments of saturated molecules.Therefore, the content of aromatics decreased from 21% to 9%, resins from 22% to 3%, and asphaltenes from 28% to 23%.The comparison between heavy oil thermal processing and catalytic thermal processing in the presence of SCW and catalysts showed a different mechanism of the upgrading process.We found that all aromatic fraction content tends to increase because of the possible cyclization of aliphatic hydrocarbons from saturated fractions.Consequently, the saturate fractions of the samples S-2, S-3, S-4, and S-5 slightly decreased.

Aromatic Fractions
The non-catalytic thermal upgrading of extra-heavy oil has revealed a decrease in aromatic content from 21% to 9%.However, the addition of SCW led to a decrease in the amount by up to 25%; meanwhile, the presence of Ni-and Co-based catalysts led to a decrease in the content less than 20%, followed by a decrease up to 23% and 30%, respectively.The supplementary increase in the content of aromatics observed in the samples of S-2, S-4, and S-5 compared to that of the extra-heavy crude oil reveals a good activity and selectivity of catalysts for cracking, the dehydrogenation of cycloalkanes, and the cyclization of some aliphatic hydrocarbons in the resins and asphaltenes; consequently, the content of the saturate fractions has slightly decreased in the presence of catalysts.On the one hand, the higher dispersity of SCW and its compatibility with hydrocarbons improved most resin and asphaltene transformations into light fractions, which increased the content of the saturated fractions to 68%.On the other hand, the catalysts played a significant role in accelerating not only the conversion of resins, but also that of asphaltenes to aromatics.This dual effect of SCW and catalysts has resulted in a significant decrease in asphaltenes from 28 wt.% to 2 wt.% because of their conversion.

Resin and Asphaltene Fractions
Resins and asphaltenes are the heaviest compounds in extra-heavy crude oil with a complex structure of molecules.It is common knowledge that their presence in thermal or catalytical upgrading processes in the refining units can cause many operational problems, such as aggregation and deposition, because they are widely considered as being the main precursor of coke formation.The decomposition of the resin fraction is most impacted by thermal upgrading, compared to hydrothermal and catalytic upgrading processes (SCW and catalysts).After the thermal and hydrothermal upgrading process of extra-heavy oil, the content of resins decreased from 22% to 3%, and then 5%.However, asphaltenes were not efficiently decomposed during thermal upgrading.It should be noted that the effective decomposition of asphaltenes can only be achieved in the presence of SCW and catalysts.In fact, the significant decrease in resin content (from 22% to 3%) observed during the thermal upgrading process (sample S-1) is related to the simultaneous decomposition and condensation of heavy free radicals to asphaltenes, and then to coke (see Figure 1).Nonetheless, the consumption of resins (from 22% to 5%) observed in the hydrothermal upgrading process in the presence of SCW is proportional to resin conversion into aromatics or saturated fractions.It is worthwhile noting that asphaltenes of the Tahe extra-heavy oil are more thermally stable in the absence of SCW and catalysts.The thermal stability of asphaltenes during non-catalytic thermal upgrading is in complete agreement with the viscosity data which showed high viscosity (135.96mPa•s) for the sample S-1, compared to that obtained for samples S-0, S-2, to S-5.

Elemental Analysis of Heavy Oil before and after Thermal, Hydrothermal, and Catalytic Upgrading
Table 1 illustrates the results of the chemical element composition (CHSN/O and Me) analysis of the studied extra-heavy crude oil before and after thermal, hydrothermal, and catalytic upgrading.It has been found that carbon redistribution trends increase in the obtained samples from thermal, hydrothermal, and catalytic upgrading processes.The maximum content of carbon (87.07%) was reached in sample S-2 in the presence of SCW.However, the redistribution of atomic hydrogen over carbon atoms during the upgrading process showed that the thermal upgrading process impacts, mainly, the cracking of C-C only and does not significantly impact the hydrogenation of carbon.This showed that the redistributed hydrogen rate by thermal upgrading does not significantly change in the upgraded oil compared to that of the initial extra-heavy crude oil (from 9.82% to 9.78%).Furthermore, our results indicated that the presence of SCW coupled with Ni-and Co-based catalysts has significantly improved the oil's properties and composition by increasing the hydrogen rate to 10.26% in the presence of SCW and to 11.69% in the presence of the used catalysts.Moreover, the relative value of H/C also showed that SCW in the presence and absence of Ni/Al 2 O 4 -, Co/Al 2 O 4 -, and Ni-CoAl 2 O 3 -based catalysts can, overall, strengthen the redistribution of the hydrogen content by stimulating hydrogenation reactions.It can cause the ionization of water as well through adsorption.This observation is completely consistent with XRD results of the used catalyst, which highlighted the ionization of water over metals as shown by AlO(OH) compounds (see Figure 14).Water ionization during the catalytic upgrading process of extra-heavy oil can strengthen the supplementary hydrogen generation for upgrading and reducing the coke formation.Additionally, the obtained data from thermal upgrading and hydrothermal upgrading in the presence of SCW and catalysts on the gas composition and elemental analysis highlight a significant gap between molecular H 2 and atomic H.The obtained data showed an increase in the H/C ratio (from 1.39 to 1.41) in the presence of SCW.However, this ratio was found to be higher in the presence of the opted catalysts, where it increased from 1.39 to 1.63.Based on the hydrogen release rate in gaseous products (shown in Figure 14 and composition redistribution in liquid products, we can assume that Ni-and Co-based catalysts can cause both simultaneous reactions of hydrogenation and dehydrogenation during the upgrading process.This phenomenon was also observed in our previous works [52].It has been found that during the extra-heavy oil catalytic upgrading process, hydrogen production can occur from the accelerated dehydrogenation of water on the surface of the catalyst.Our results indicate that heteroatom and metal (S, N, Me + O) contents also tend to decrease in the obtained samples from thermal and hydrothermal upgrading processes in the presence and absence of catalysts.Sulfur content has significantly decreased from 1.84% in extra-heavy crude oil to 1.42% in sample S-1, and then to 1.35% in sample S-5.The mechanism of sulfur removal from both samples (S-1 and S-5) is supposed to be different.For sample S-1, the sulfur is removed by a radical mechanism, where the resulting free radicals from thermal processing undergo recombination; meanwhile, the high-molecular-weight heteroatomic hydrocarbons occur through polymerization during coke formation.Detecting CoNi 3 S 4 compounds in XRD patterns of the used catalyst (see Figure 11) points toward the idea that the sulfur removal from extra-heavy oil of sample S-5 during the catalytic upgrading process can take place only by oxidative and adsorptive desulfurization mechanisms.This mechanism is similar to that of the oxygen+metal removal from oil.

Aromatic Identification in the Upgraded Oil by GC-MS
Table 2 elucidates the results of the aromatic content analysis in the initial extra-heavy crude oil and the upgraded oil samples obtained from thermal, hydrothermal (SCW), and catalytic processes via GC-MS analysis.The obtained results of GC-MS of the upgraded products are subdivided into mono-, di-, and polyaromatic fractions.According to GC-MS results, the thermal upgrading of extra-heavy oil is characterized by two different pathways: the first includes the C-C thermal cracking reaction, and the second one includes the cleavage of C-S bonds in resin fractions.The obtained data indicate that the content of n-alkanes increased from 0.67% to 23.30% and the polymerization of diaromatics led to an increase in polyaromatics from 37.46% to 48.98%.Additionally, these results agree with the results of the SARA analysis, which revealed a significant decrease in resins to aromatics and asphaltenes.Moreover, monoaromatic fractions abruptly increased from 4.22% to more than 35% in the presence of SCW, and CoAl 2 O 4 and Ni-CoAl 2 O 3 catalysts, at the expense of polyaromatic fractions which decreased from 37.46% to 10%.The significant decrease in polyaromatics contributes to the monoaromatic increase, as indicated by samples S-2, S-4, and S-5.This increase in monoaromatics is related to the conversion of some alkanes and polyaromatic fractions into mono-and diaromatic fractions through the cyclization of aliphatics, and into gaseous products via the hydrothermal and catalytic cracking of asphaltenes, respectively.The obtained data about the significant conversion of polyaromatics into mono-and diaromatic fractions in samples S-2, S-3, and S-5 are in a good agreement with the results obtained in [52][53][54].Contrary to samples S-2, S-3, and S-5, samples S-1 and S-4 showed a different effect of the upgrading process on alkane's fraction content, which increased because of cracking and alkylation of aliphatic fragments.The slightly higher content of polyaromatics in samples S-1 and S-4 confirms the results of the upgraded oil's viscosity, which showed slightly higher values than other samples.

Materials
The studied extra-heavy crude oil sample in this paper was obtained from Tahe Oil Field and kindly provided by the Sinopec Company (Beijing, China).The sample was extracted from deeper reservoirs at more than 5500 m using a gas injection technique.Nheptane (99.6%), toluene (99.8%), chloroform, and isopropyl alcohol (99.5%) were provided by the Eco.1 Company (Saint-Petersburg, Russia).The characteristics, properties, and composition of the heavy crude oil from the Ashal'cha Oil Deposit can be found in Table 3.

Analytical Methods
The carbon number distribution of the saturate fractions and the composition and yield of evolved gases after hydrothermal upgrading processes, including hydrocarbons gases (C 1 -C 4 ), hydrogen (H 2 ), hydrogen sulfur (H 2 S), monoxide carbon (CO), dioxide carbon (CO 2 ), and nitrogen (N 2 ), were determined using Agilent 7890A gas chromatography (GC, Santa Clara, CA, USA) with a flame ionization detector (FID) and gas chromatography (Chromatec Crystal 5000.2,Chromatec, Yoshkar-Ola, Russia), respectively.The viscosity and density of the heavy crude oil and upgraded oil samples [53] were measured via the Brookfield DV-II + Pro (Fungilab, Barcelona, Spain) and SVM 3000t (Anton Paar, Graz, Austria) viscometers [54].The elemental composition (C, H, N, and S) of the initial and upgraded oil samples was analyzed via the PE 2400 Series II CHNS/O Analyzer (PerkinElmer, Waltham, MA, USA) [53].The composition fraction of saturated hydrocarbons, aromatics, resins, and asphaltenes (SARA) was performed according to ASTM D 4124.The aromatic fractions of the heavy crude oil and upgraded oil samples were measured via a gas chromatography/mass spectrometer GC-MS, which included the gas chromatograph, "Chromatec Crystal 5000", with an ISQ mass-selective detector (Thermo Fisher Scientific, Waltham, MA, USA).Xcalibur software (Thermo Fisher Scientific, Waltham, MA, USA) was used to process the results.The chromatograph is equipped with a capillary column that has a 30 m length and 0.25 mm diameter.The rate at which the carrier gas (helium) flow was performed was 1 mL/min.The injector temperature was 310 • C. The thermostat temperature program was as follows: temperature increase from 100 to 150 • C at a rate of 3 • C/min and from 150 to 300 • C at a rate of 12 • C/min, followed by its isotherm until the end of the analysis.The electron energy of the mass detector was 70 eV; the ion source temperature was 250 • C. Compounds were identified through the electronic library of the NIST spectra database and based on data from literature sources [53].The resin and asphaltene fractions were determined using a Bruker AVANCE-III-HD-500 NMR spectrometer (Bruker, Billerica, MA, USA) [55].

Catalyst Characterization
In order for us to be able to study the structure, morphology, and surface propertie of the obtained catalysts, we applied a method of analysis which combined X-ray diffrac tion (XRD), SEM, TEM, and BET analyses.This method was chosen because it is one o the most practical methods applied in studying catalysts' morphological and structura properties.

Catalyst Characterization
In order for us to be able to study the structure, morphology, and surface properties of the obtained catalysts, we applied a method of analysis which combined X-ray diffraction (XRD), SEM, TEM, and BET analyses.This method was chosen because it is one of the most practical methods applied in studying catalysts' morphological and structural properties.

XRD Analysis
XRD measurements were carried out on the MD-10 desktop diffractometer (Rodicon, Saint Petersburg, Russia) using Fe Kα radiation (λ = 1.93728Å) in the Debye-Scherrer geometry.The obtained XRD data of the opted catalysts before and after hydrothermal processing of heavy oil, in addition to coke, are presented in Figures 6 and 7.

Catalyst Characterization
In order for us to be able to study the structure, morphology, and surface propertie of the obtained catalysts, we applied a method of analysis which combined X-ray diffrac tion (XRD), SEM, TEM, and BET analyses.This method was chosen because it is one o the most practical methods applied in studying catalysts' morphological and structura properties.

XRD Analysis
XRD measurements were carried out on the MD-10 desktop diffractometer (Rodicon Saint Petersburg, Russia) using Fe Kα radiation (λ = 1.93728Å) in the Debye-Scherre geometry.The obtained XRD data of the opted catalysts before and after hydrotherma processing of heavy oil, in addition to coke, are presented in Figures 6 and 7.

SEM/TEM Analyses
In order to study the composition and morphology of the obtained catalysts, we used FESEM (Merlin Carl Zeiss, Oberkochen, Germany) equipped with an Aztec X-MAX en ergy dispersive spectrometer (Oxford Instruments, Abingdon, UK).The morphologica structure and surface analysis were taken at an accelerating voltage of 5 keV and a probe current of 300 pA.Moreover, the microprobe elemental analysis was performed at an ac celerating voltage of 20 keV and the sounding depth was about 1 µm.The SEM images and spectra of the obtained catalysts are presented in Figures 8-10.

SEM/TEM Analyses
In order to study the composition and morphology of the obtained catalysts, we used FESEM (Merlin Carl Zeiss, Oberkochen, Germany) equipped with an Aztec X-MAX energy dispersive spectrometer (Oxford Instruments, Abingdon, UK).The morphological structure and surface analysis were taken at an accelerating voltage of 5 keV and a probe current of 300 pA.Moreover, the microprobe elemental analysis was performed at an accelerating voltage of 20 keV and the sounding depth was about 1 µm.The SEM images and spectra of the obtained catalysts are presented in Figures 8-10.
In order to study the composition and morphology of the obtained catalysts, we used FESEM (Merlin Carl Zeiss, Oberkochen, Germany) equipped with an Aztec X-MAX energy dispersive spectrometer (Oxford Instruments, Abingdon, UK).The morphological structure and surface analysis were taken at an accelerating voltage of 5 keV and a probe current of 300 pA.Moreover, the microprobe elemental analysis was performed at an accelerating voltage of 20 keV and the sounding depth was about 1 µm.The SEM images and spectra of the obtained catalysts are presented in Figures 8-10.In order to study the composition and morphology of the obtained catalysts, we used FESEM (Merlin Carl Zeiss, Oberkochen, Germany) equipped with an Aztec X-MAX energy dispersive spectrometer (Oxford Instruments, Abingdon, UK).The morphological structure and surface analysis were taken at an accelerating voltage of 5 keV and a probe current of 300 pA.Moreover, the microprobe elemental analysis was performed at an accelerating voltage of 20 keV and the sounding depth was about 1 µm.The SEM images and spectra of the obtained catalysts are presented in Figures 8-10.The specific surface area, pore volumes, and their distribution over pore diameters were determined on an ASAP 2400 analyzer from Micromeritics (Norcross, GA, USA).The value of specific surface area was determined by the thermal desorption of nitrogen

Analyses and Determination of Specific Surface Area and Pore Volume
The specific surface area, pore volumes, and their distribution over pore diameters were determined on an ASAP 2400 analyzer from Micromeritics (Norcross, GA, USA).The value of specific surface area was determined by the thermal desorption of nitrogen with a ±3% measurement accuracy and calculated by assuming the nitrogen molecule's surface area as being equal to 0.162 nm 2 .The density of nitrogen in the normal liquid state is 0.808 g/cm 3  On the other hand, we used a transmission electron microscope (TEM) Hitachi HT7700 Exalens (Hitachi Ltd.Tokyo, Japan) to illustrate the internal and external morphological structure of the obtained catalyst samples by placing 10 microliters of the suspension on a formvar/carbon lacey 3 mm copper grid, followed by drying at room temperature.After drying, the grid was placed under a transmission electron microscope using a special holder for microanalysis.After that, the analysis was performed at an accelerating voltage of 100 kV in TEM mode.Finally, the elemental analysis was carried out in STEM mode, at the same parameters using the Oxford Instruments X-Max™ 80T detector (Abingdon, UK).The obtained TEM images for the studied catalysts are shown in Figures 11 and 12.      SEM and TEM analysis results (Table 4) showed 3.55% of cobalt (Co) in the Co/Al2O4 catalyst, and 12.15% of nickel (Ni) in the Ni/Al2O4 catalyst.Moreover, the Ni-CoAl2O3 alloy catalyst contained 2.71% of Ni and 1.69% of Co.Although the catalysts were synthesized by the same method, the large difference observed in the average sizes also depends on the composition of the catalysts, as can be seen in Table 4. Therefore, the catalyst average particle size is 37.0355, 944.33, and 874.8551 nm (see Table 5).In this article, we investigated the effect of cobalt, nickel, and the cobaltnickel metal alloy on the refining process of extra-heavy oil.However, it is clear that the introduction of cobalt-nickel into the catalysts leads to an increase in the activity of the catalysts.The method of low-temperature nitrogen adsorption actually makes it possible to estimate the size of the pores that are formed during the coordination of catalyst particles.Since these pores are formed by catalyst particles, the mathematical techniques used can be also used to determine the average particle size.Thus, the low-temperature nitrogen adsorption method is based on filling (adsorption) of the pores with liquid nitrogen.Although the catalysts were synthesized by the same method, the large difference observed in the average sizes also depends on the composition of the catalysts, as can be seen in Table 4. Therefore, the catalyst average particle size is 37.0355, 944.33, and 874.8551 nm (see Table 5).In this article, we investigated the effect of cobalt, nickel, and the cobalt-nickel metal alloy on the refining process of extra-heavy oil.However, it is clear that the introduction of cobalt-nickel into the catalysts leads to an increase in the activity of the catalysts.The method of low-temperature nitrogen adsorption actually makes it possible to estimate the size of the pores that are formed during the coordination of catalyst particles.Since these pores are formed by catalyst particles, the mathematical techniques used can be also used to determine the average particle size.Thus, the low-temperature nitrogen adsorption method is based on filling (adsorption) of the pores with liquid nitrogen.Prior to measurement, the sample is cooled to a temperature at which the transition from gaseous N 2 to the liquid phase occurs.The size, volume, and surface area of catalysts are the most important characteristics to determine before and after the upgrading processes of heavy crude oil.Figures 13 and 14 show the BJH adsorption and desorption curves of the pore distribution of the Co/Al 2 O 4 and Ni/Al 2 O 4 catalysts.Additionally, Figure 15 presents the curves of BJH adsorption and desorption (pore volumes) of the Ni-CoAl 2 O 3 catalyst.Although the catalysts were synthesized by the same method, the large difference observed in the average sizes also depends on the composition of the catalysts, as can be seen in Table 4.These catalysts really have different sizes, where the average particle size is 37.0355, 944.33, and 874.8551 nm.In this article, we investigated the effect of cobalt, nickel, and the cobalt-nickel metal alloy on the refining process of extra-heavy oil.However, it is clear that the introduction of cobaltnickel into the catalysts leads to an increase in the activity of the catalysts.According to TEM and SEM analysis, the average particle size of the Co/Al 2 O 4 , Ni/Al 2 O 4 , and Ni-CoAl 2 O 3 catalysts is 0.62, 1.85, and 1.07 µm, respectively.According to the BJH curves, it should be indicated that for catalysts, pore diameters ranging from 10 to 60 nm have desorption values dropping from 0.00057 cm 3 /g•nm to 0.00015 cm 3 /g•nm.Similarly, Figure 15 shows the BJH curves of adsorption desorption of Ni-CoAl 2 O 3 .It has been observed that the diameter pores ranged from 6 to 80 nm of the catalyst, showing the pore volume value of 0.0009 cm 3 /g•nm, and the range of 80-120 nm showed from 0.0005 cm 3 /g•nm to 0.0001cm 3 /g•nm of the diameter pores.
Desorption pore diameter (4V/A by BET), nm 11.758 7.999 9.457 The size, volume, and surface area of catalysts are the most important characteristics to determine before and after the upgrading processes of heavy crude oil.Figures 13 and Figure 14 show the BJH adsorption and desorption curves of the pore distribution of the Co/Al2O4 and Ni/Al2O4 catalysts.Additionally, Figure 15 presents the curves of BJH adsorption and desorption (pore volumes) of the Ni-CoAl2O3 catalyst.Although the catalysts were synthesized by the same method, the large difference observed in the average sizes also depends on the composition of the catalysts, as can be seen in Table 4.These catalysts really have different sizes, where the average particle size is 37.0355, 944.33, and 874.8551 nm.In this article, we investigated the effect of cobalt, nickel, and the cobalt-nickel metal alloy on the refining process of extra-heavy oil.However, it is clear that the introduction of cobalt-nickel into the catalysts leads to an increase in the activity of the catalysts.According to TEM and SEM analysis, the average particle size of the Co/Al2O4, Ni/Al2O4, and Ni-CoAl2O3 catalysts is 0.62, 1.85, and 1.07 µm, respectively.According to the BJH curves, it should be indicated that for catalysts, pore diameters ranging from 10 to 60 nm have desorption values dropping from 0.00057 cm 3 /g•nm to 0.00015 cm 3 /g•nm.Similarly, Figure 15 shows the BJH curves of adsorption and desorption of Ni-CoAl2O3.It has been observed that the diameter pores ranged from 6 to 80 nm of the catalyst, showing the pore volume value of 0.0009 cm 3 /g•nm, and the range of 80-120 nm showed from 0.0005 cm 3 /g•nm to 0.0001cm 3 /g•nm of the diameter pores.The obtained data from the surface area and volume pore analysis are summarized in Table 5.

Extra-Heavy Oil Hydrothermal Processing Experiments
Our experimental procedure of the thermocatalytic upgrading of extra-heavy oil in SCW was practically the same as the one proposed in our previous work [52].The thermocatalytic experiments were performed at 420 ± 1 • C for 120 min (2 h) by inserting 75 ± 0.002 g of extra-heavy crude oil and 75 ± 0.002 g of distilled water into a high-pressure batch reactor under a static regime.Then, 2.00 wt.% of the investigated catalyst was added to the feedstock.An initial pressure of 5 bars at 25 • C was set in the reactor after removing air from the reactor by nitrogen injection.A detailed description of the separation procedure of gas-liquid-solid products can be found in our previous works.The terms S-0, S-1, S-2, S-3, S-4, and S-

Conclusions
A range of hydrogen production catalysts were synthesized and their effects on the hydrothermal upgrading of extra-heavy crude oil from the Chinese Tahe Oil Deposit were investigated.The acquired catalysts were characterized using a variety of physical and chemical ways before being used to upgrade the examined oil using various processing methods in the presence and absence of SCW.The examined catalysts had surface areas ranging from 3.04 to 162 m 2 /g and average sizes ranging from 0.037 to 0.944 m.The yields of molecular hydrogen rose in the presence of SCW and catalysts, increasing from 1.0598 mol.% in the absence of SCW to 6.1320 mol.% in its presence, with a maximum yield of 11.78 mol.% in the presence of SCW and Ni-Co/Al 2 O 3 catalysts.Furthermore, our findings demonstrate that the dramatic increase in hydrogen yields in the presence of SCW and catalysts is due to steam methane reforming and water-gas shift processes that occur throughout the upgrading process.Furthermore, the catalytic upgrading demonstrated a good performance for heteroatom removal via radical and oxidative processes, as evidenced by a decrease in sulfur from 1.84 to 1.35 wt.%.As a result, the viscosity of the improved oil samples fell from 61 × 10 6 mPas in the absence of SCW and catalysts to 3.72 mPas in their presence.Interestingly, SCW and catalytic upgrading performed well in the cleavage of C-C and C-H bonds in resin and asphaltene fractions, reducing the number of asphaltenes from 28% to 2%.Another benefit of SCW and the synthetized catalysts is a decrease in coke yield, which was found to reduce from 51.02 wt.% in the absence of SCW and catalysts to

Figure 1 .
Figure 1.Yield of hydrogen after hydrothermal upgrading of extra-heavy oil.

Figure 1 .
Figure 1.Yield of hydrogen after hydrothermal upgrading of extra-heavy oil.

Figure 2 .
Figure 2. Hydrogen to monoxide carbon ratio after H 2 /CO and H 2 /CO 2 .

Figure 3 .
Figure 3. Yield of hydrogen after hydrothermal upgrading of extra-heavy oil.

Figure 4 .
Figure 4. SARA analysis of extra-heavy oil and upgraded oil samples.

Figure 3 .
Figure 3. Yield of hydrogen after hydrothermal upgrading of extra-heavy oil.

Figure 3 .
Figure 3. Yield of hydrogen after hydrothermal upgrading of extra-heavy oil.

Figure 4 .
Figure 4. SARA analysis of extra-heavy oil and upgraded oil samples.

Figure 4 .
Figure 4. SARA analysis of extra-heavy oil and upgraded oil samples.

Figure 6 .
Figure 6.XRD patterns of the obtained catalysts.

Figure 7 .
Figure 7. XRD patterns of the fresh catalysts and coke.

Figure 9 .
Figure 9. Morphological structure of Ni-CoAl2O3 obtained from SEM.Figure 9. Morphological structure of Ni-CoAl 2 O 3 obtained from SEM.
. Nitrogen adsorption isotherms were obtained at T = −196 • C after sample degassing at T = 500 • C to a residual pressure of 0.013 Pa.The calculations of the parametric volume and the distribution of pore volumes by diameters were carried out using the desorption branch of the isotherm according to the standard Barrett-Joyner-Halenda procedure with a ±13% measurement accuracy.XRD patterns revealed that the obtained catalysts consist of Co/Al 2 O 4 , Ni/Al 2 O 4 , and Ni-CoAl 2 O 3 and a non-significant part of Co 3 O 4 .The obtained data revealed the main features as well in the 2θ range of 30-35 • .There are two bands, namely, the γ-band and C [002] band.In analogy with asphaltenes [56], the γ-band is connected to spacing between condensed saturated structures, whereas the C [002] band is connected to spacing between aromatic layers.From the relationship of these bands with each other, we may make the conclusion about the "aromaticity" of petroleum coke.It is seen that the C [002] band is almost absent on the XRD pattern of coke without a catalyst.However, with the addition of the Al 2 O 3 -based catalyst, this band manifests itself, and has maximal intensity on the XRD pattern of coke with the Co-Al 2 O 4 catalyst.We suppose that other small reflexes may be related with sulfides of Ni and Co.A broad reflex at 2θ ≈ 58 • on XRD patterns of cokes with catalysts may relate to the amorphous form of Al 2 O 4 .

Catalysts 2022 ,
12, 1183 14 of 19 the same parameters using the Oxford Instruments X-Max™ 80T detector (Abingdon, UK).The obtained TEM images for the studied catalysts are shown in Figures11 and 12 .

Figure 11 .
Figure 11.Morphological structure of Co/Al2O4 (A) and Ni/Al2O4 (B) obtained from TEM.Figure 11.Morphological structure of Co/Al 2 O 4 (A) and Ni/Al 2 O 4 (B) obtained from TEM. SEM and TEM analysis results (Table 4) showed 3.55% of cobalt (Co) in the Co/Al 2 O 4 catalyst, and 12.15% of nickel (Ni) in the Ni/Al 2 O 4 catalyst.Moreover, the Ni-CoAl 2 O 3 alloy catalyst contained 2.71% of Ni and 1.69% of Co.

Figure 13 .
Figure 13.BJH adsorption and desorption of pore volume of Co/Al2O4 catalyst.Figure 13.BJH adsorption and desorption of pore volume of Co/Al 2 O 4 catalyst.
5 will be used to refer to the sample of extra-heavy crude oil (Tahe oil), sample without SCW, sample with SCW, sample with SCW + Co/Al 2 O 4 , sample with SCW + Ni/Al 2 O 4 , and sample with SCW + Ni-CoAl 2 O 3 , respectively.

Table 1 .
Results of elemental composition of initial and upgraded oils.
* is determined by difference.

Table 2 .
Composition and content of aromatic fractions of heavy oil and upgraded oil samples.

Table 3 .
Viscosity, density, SARA fractions, and elemental analysis of the studied heavy crude oil.
a Rotational viscometer (Brookfield DV-II Pro) was used according to ASTM D-4124.

Table 4 .
The chemical composition content of the obtained catalysts.

Table 4 .
The chemical composition content of the obtained catalysts.

Table 5 .
Characteristics of mono-and bimetallic catalysts using the micrometry method.