Hydrodeoxygenation Of Bio-oil Research Articles

Targeted preparation for hydrocarbons through catalytic hydrodeoxygenation of co-pyrolysis bio-oil using bimetal-loaded Nb2O5 catalyst

The co-pyrolysis of industrial enzymatic hydrolysis of lignin residue with waste plastic to produce bio-oil can increase resource utilization and reduce pollution. However, the high concentration of oxygenated compounds, particularly phenolic compounds, limits the large-scale application of crude bio-oil. Bimetallic-loaded bifunctional catalysts have been prepared by loading different transition metals and Ru onto Nb2O5. We explored their performances in crude co-pyrolysis bio-oil hydrodeoxygenation (HDO). Compared to other transition metals, the selectivities for aromatic hydrocarbons, phenolic compounds, and other oxygenated compounds in the upgraded oil obtained by the catalytic HDO of Ni and Ru bimetallic-loaded Nb2O5 (Ni-Ru@Nb2O5) was the lowest, whereas the aliphatic hydrocarbons selectivity was the highest. The selectivities for other oxygenated compounds, phenolic compounds, and aromatic hydrocarbons in the upgraded oil decreased as the Ni loading increased, whereas the aliphatic hydrocarbons selectivity increased. Ni-Ru@Nb2O5 catalyzed HDO of crude bio-oil showed a maximum selectivity of 86.30 % for hydrocarbons in the upgraded oil at a reaction time of 2 h and a reaction temperature of 280 °C. The degree of deoxygenation of upgraded oil reached 68.87 % under optimal conditions, and the molar ratio of H-to-C was increased from 1.31 (crude bio-oil) to 2.37 (upgraded oil). Ni-Ru@Nb2O5 is an effective catalyst method for the HDO of crude bio-oil.

Phyllosilicate-derived Ni/SiO2 catalyst for liquid-phase hydrodeoxygenation of phenol: Synergy of Lewis acid sites and Ni0

Designing effective catalysts using non-noble metals for bio-oil hydrodeoxygenation (HDO) into liquid fuels is greatly sought after, yet it remains a great challenge. Contrary to the prevailing belief that monometallic nickel lacked activity in the HDO of oxygen-containing compounds, this study demonstrates a remarkable catalytic performance over monometallic Ni catalyst. Herein, a Ni/SiO2 catalyst having both nickel phyllosilicate and Ni0 was synthesized by the ammonia evaporation (AE) method. The Ni-PS-400 catalyst reduced at 400 ℃ achieves a significant high activity and yields 97 % cyclohexane at a low reaction temperature of 190 ℃, surpassing both Ni-IMP-400 prepared by impregnation method and most of the reported other non-noble metal catalysts which are generally used at high temperature of above 240 ℃. It was found that the reduction temperature of Ni-PS-X influences the catalytic activity, as more dispersed Ni nanoparticles and acidic sites can be produced on the surface of the support at an appropriate temperature. The outstanding catalytic performance can be ascribed to the collaborative effect of well-scattered Ni nanoparticles and the significant presence of Lewis acidic sites, which result from coordinatively unsaturated Ni2+ sites situated within the remaining nickel phyllosilicate.

Tailoring and Visualizing Macropores of the Zeolite Monolith to Reveal the Coke Resistance Performance for Bio-oil Hydrodeoxygenation

Tailoring and Visualizing Macropores of the Zeolite Monolith to Reveal the Coke Resistance Performance for Bio-oil Hydrodeoxygenation

Production of Valuable Aromatics from the Hydrodeoxygenation of Guaiacol and Real Bio-Oil over Ni–Nb/HZSM-5 under Supercritical Ethanol

Production of Valuable Aromatics from the Hydrodeoxygenation of Guaiacol and Real Bio-Oil over Ni–Nb/HZSM-5 under Supercritical Ethanol

Selective production of high-value fuel via catalytic upgrading of bio-oil over nitrogen-doped carbon-alumina hybrid supported cobalt catalysts

Bio-oil derived from biomass fast pyrolysis can be upgraded to gasoline and diesel alternatives by catalytic hydrodeoxygenation (HDO). Here, the novel nitrogen-doped carbon–alumina hybrid supported cobalt (Co/NCAn, n = 1, 2.5, 5) catalyst is established by a coagulation bath technique. The optimized Co/NCA2.5 catalyst presented 100 % conversion of guaiacol, high selectivity to cyclohexane (93.6 %), and extremely high deoxygenation degree (97.3 %), respectively. Therein, the formation of cyclohexanol was facilitated by stronger binding energy and greater charge transfer between Co and NC which was unraveled by density functional theory calculations. In addition, the appropriate amount of Lewis acid sites enhanced the cleavage of the C–O bond in cyclohexanol, finally resulting in a remarkable selectivity for cyclohexane. Finally, the Co/NCA2.5 catalyst also exhibited excellent selectivity (93.1 %) for high heating value hydrocarbon fuel in crude bio-oil HDO. This work provides a theoretical basis on N dopants collaborating alumina hybrid catalysts for efficient HDO reaction.

Tuning of the acid sites in the zeolite-alumina composite Ni catalysts and their impact on the palm oil hydrodeoxygenation reaction

The hydrodeoxygenation (HDO) of bio-oil is one of the potential approaches to produce green diesel. However, HDO catalyst requires the development of bifunctionality which translates to the simultaneous presence of acidic and metal sites for desired catalytic activity and selectivity. Zeolites and their composites are attractive candidates for the conversion of biomass to fuels. In the present work, a series of Ni-incorporated Al2O3-zeolite beta bifunctional composite catalysts with distinct Al2O3 (25–75 wt%) and Ni contents (5–15 wt%) were synthesized via a facile one-pot method directly from nickel acetate, nano-boehmite (γ-AlO(OH)) and the NH4+ form of beta zeolite (NH4+-BZ). The nano-boehmite particles, due to the positive charges on their surface, electrostatically attract negatively charged beta zeolite crystals, which leads to the assembly of a hierarchical pore structure upon calcination. Interestingly, the composite catalysts synthesized were quite homogeneous with uniform dispersion of Ni particles. All composite catalysts were thoroughly characterized using XRD, SEM-EDX, SEM-mapping, HR-TEM, H2-TPR, H2-TPD, NH3-TPD, XPS, 31P MAS NMR, 27Al MAS NMR and N2 sorption analysis. The synthesized composite catalysts with distinct Al2O3 contents showed diverse textural properties, distinct nature of acid sites and improved performance in hydrodeoxygenation of palm oil. Particularly, the Ni/BZ-Al50 (with BZ:Al2O3 = 50:50) composite catalyst significantly enhanced the conversion of palm oil (up to 90%) and yield of n-C15-C18 hydrocarbons (up to 69%) at moderate temperature of 375 °C as compared to 10Ni/BZ catalyst (Conv. = 75%, yield of n-C15-C18 = 52%). The higher catalytic performance realized with composite catalysts can be ascribed to its hierarchical pore structure, moderate acidity (chemisorption studies), tuned acid sites nature (solid state NMR) and homogeneous distribution of active Ni sites (H2 chemisorption) which helps to improve product selectivity by minimizing side reactions. The time-on-stream (TOS) experiments were carried out up to 20 h which clearly showed that composite catalysts are more stable suggesting the lower amount of coke deposition (TPO studies) and suppression of metal sintering.

Co-ZIF reinforced kraft lignin biochar as an efficient catalyst for highly selective hydrodeoxygenation of lignin-derived chemicals

Large amount of lignin was produced annually as a byproduct in papermaking and pulping processes, the challenges in disposal methods had posed serious obstacles for advanced carbon materials and value-added chemicals. This study involved the preparation of kraft lignin (KL) loaded metal–organic framework (ZIF-67) material derived Co nanoparticles carbon using various methods to produce kraft lignin biochar-based carbon materials (Co@NPC-KLB). The novel and advanced carbon materials was utilized for lignin derived bio-oil hydrodeoxygenation to generate high value fuels and chemicals. It could achieve nearly 100 % vanillin (VAN) conversion and 88.49 % 2-methoxy-4-methylphenol (MMP) without the extra hydrogen at 240 °C in ethanol. The results demonstrated that highly active and stable Co nanoparticles, large specific surface area, smaller nano Co nanoparticles, strong metal-support interaction and rich Lewis acid sites on the surface of biochar support exhibited a positive promoting effect on VAN hydrodeoxygenation to generate MMP. Furthermore, density functional theory (DFT) also confirmed that synergistic effect of Co nanoparticles and kraft lignin biochar promoted a high adsorption energy of VAN on the surface of kraft lignin biochar, enhanced the catalytic ability of the hydrodeoxygenation process. This study provided a novel approach for utilizing kraft lignin in preparation functional catalysts, opening up new opportunities for designing efficient biochar-based materials for advanced carbon materials and high-value chemicals.

Catalytic hydrodeoxygenation of pyrolysis bio-oil to jet fuel: A review

Catalytic hydrodeoxygenation of pyrolysis bio-oil to jet fuel: A review

Cs-promoted hydrogenation upgrading of bio-oil over macroporous Ru-containing catalysts using model compounds

Hydrogenation upgrading is an effective technique that lowers the oxygen content of bio-oil with the aim of improving its quality. In order to fabricate a series of Ru-based catalysts for the hydrodeoxygenation of bio-oil, several all-silica supports with different pore sizes are synthesized and modified with Al and Cs in this work. The physical morphology and electronic structure of the catalysts are characterized using multiple techniques including X-ray diffraction, in-situ pyridine adsorption infrared spectroscopy, in-situ diffuse reflectance Fourier transform infrared spectroscopy, Raman spectroscopy, CO2 temperature-programmed desorption, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and N2 physical adsorption-desorption testing. Phenol, guaiacol, anisole and o-cresol are selected as model compounds to investigate the hydrodeoxygenation reactivity of the catalysts. The results reveal that there is a strong linear correlation between the pore size of the catalysts and the rates of the hydrogenation and hydrodeoxygenation of phenol. Importantly, both the oxygen vacancy density and relative content of Brønsted and Lewis sites (B/L) of the catalysts can be greatly increased by Cs modification, which further linearly promotes the hydrodeoxygenation activity of the catalysts. In addition, the in-situ infrared spectroscopy results show that the catalysts modified by Al and Cs heterolytically cleave H2 to supply H+ for the reaction. This work presents a novel approach for fabricating catalysts employed in the hydrotreatment process of bio-oil.

In situ hydrodeoxygenation of heavy bio-oil using a Ce/Fe-based oxygen carrier in methanol-zero valent aluminum media

Resource recovery from solid organic wastes, such as degradable plastics, and upgrading raw bio-oil are important ways for reducing carbon and pollution emissions. Hydrodeoxygenation (HDO) is a common thermochemical treatment to upgrade crude bio-oil. In this study, in order to realize in situ HDO during the hydropyrolysis of heavy bio-oil and degradable plastics, a reduced Fe/Ce oxygen carrier (OC) was used to catalytically remove oxygen from organics under the methanol-zero valent aluminum (ZV Al) media, where the hydrogen was produced during pyrolysis instead of a direct hydrogen supply. The results showed that the reduced OC captured the oxygen from the pyrolysis products of heavy bio-oil and degradable plastic, representing the multi-selectivity of reduced OC to phenols, ketones, etc. The ZV Al system promoted the production and utilization of hydrogen, as evidenced by the increased hydrogen content in gas phase and hydrocarbon content in liquid phase. The hydrocarbon component distribution in the liquid phase increased clearly when hydropyrolysis with degradable plastics addtion, but the excess degradable plastics addition caused increasing of the liquid product viscosity, and decreasing of the liquid products yield for the higher ash content in degradable plastic, and a higher ZV Al amount was required to maintain the hydropyrolysis. Molecular dynamics simulations verified the synergistic effect of degradable plastics and bio-oil by the pyrolysis behavior in different systems and temperatures, and the pyrolysis pathways were proposed. This non-autocatalytic system realized the resource recovery and heavy bio-oil upgrading using an Fe/Ce OC.

Catalytic Hydrodeoxygenation of Solar Energy Produced Bio-Oil in Supercritical Ethanol with Mo2C/CNF Catalysts: Effect of Mo Concentration

Transition metal carbides have emerged as an attractive alternative to conventional catalysts in hydrodeoxygenation (HDO) reactions due to surface reactivity, catalytic activity, and thermodynamic stability similar to those of noble metals. In this study, the impact of varying Mo concentration in carbon nanofiber-supported catalysts for the supercritical ethanol-assisted HDO of bio-oils in an autoclave batch reactor is discussed. Raw bio-oils derived from agave bagasse and corncob through solar hydrothermal liquefaction were treated at 350 °C. Our findings indicate that the presence of Mo has a strong impact on both product yield and chemical properties. Thus, a Mo concentration of 10 wt.% is enough to obtain high deoxygenation values (69–72%), resulting in a yield of upgraded bio-oil ranging between 49.9 and 60.4%, depending on the feedstock used, with an energy content of around 35 MJ/kg. A further increase in the Mo loadings (20 and 30 wt.%) reduced the loss of carbon due to gasification and improved the bio-oil yields up to 62.6 and 67.4%, without compromising the product quality.

Evaluation of Bio-Oils in Terms of Fuel Properties

In response to the global climate challenge and the increasing demand for energy, exploring renewable energy alternatives has become crucial. Bio-oils derived from biomass pyrolysis are emerging as potential replacements for fossil fuel-based liquid fuels. This paper shares findings from the Institute of Energy and Fuel Processing Technology on the quality of crude biomass pyrolysis bio-oil samples. These findings highlight their potential as motor liquid fuels. The article details the results of tests on the physicochemical properties of four distinct bio-oil samples. Additionally, it presents preliminary test results on the hydrodeoxygenation of bio-oils in a batch reactor. The production of homogeneous, stable mixtures using other fuel additives, such as diesel oil, rapeseed methyl ester (RME), and butanol, is also discussed.

Understanding the role of Ni-based single-atom alloys on the selective hydrodeoxygenation of bio-oils

In the search for sustainable fuels, high-performing, cost-effective, and abundant catalysts are needed for bio-oils hydrodeoxygenation refining, with single-atom-alloy (SAA) catalysts showing potential for outstanding activity and economic bi-metallic assembly. Hydrodeoxygenation upgrading of modelled bio-oil molecules, namely, phenol, anisole, benzaldehyde, and vanillin, has been systematically explored here over a wide-range of SAA Ni(111)-based catalysts (Pd, Pt, Cu, Co, Fe, Ru, Re, Rh, V, W, and Mo) using density functional theory (DFT) and microkinetic modeling. Stability, adsorptive, and activity structural-property-relationships were established for bio-oil derivatives that can direct the synthesis process of cost-effective SAA combinations. DFT revealed the thermodynamic atomic dispersion tendency of the SAA catalysts. Furthermore, the OH*- and O*−induced on the catalyst surface enhanced the SAA upper-layer stability. Single-atoms shifted the d-band center towards the fermi-level in agreement with bio-oils adsorption energies and Caryl−O lengths. The free-energy pathways at 573 K unveiled the SAAs role in lowering the activation barriers, with WNi(111) best-performing towards selective phenol and anisole direct deoxygenation, whilst MoNi(111) directs the facile activation of benzaldehyde and vanillin CO scission. The microkinetic/thermodynamic analysis of O*-poisoning showed that MoNi(111) withstands high O*-coverage, indicative by higher deoxygeneration rates in 350-950 K and greater coverage of the desired product.

Linear Scaling Relationships for Furan Hydrodeoxygenation over Transition Metal and Bimetallic Surfaces.

Brønsted-Evans-Polanyi (BEP) and transition-state-scaling (TSS) relationships have become valuable tools for the rational design of catalysts for complex reactions like hydrodeoxygenation (HDO) of bio-oil (containing heterocyclic and homocyclic molecules). In this work, BEP and TSS relationships are developed for all the elementary steps of furan activation (C and O hydrogenation and CHx -OHy scission, for both ring and open-ring intermediates) to oxygenates, ring-saturated compounds and deoxygenated products on the most stable facets of Ni, Co, Rh, Ru, Pt, Pd, Fe and Ir surfaces using Density Functional Theory (DFT) calculations. Furan ring opening barriers were found to be facile and strongly dependent on carbon and oxygen binding strength on the investigated surfaces. Our calculations suggest linear chain oxygenates form on Ir, Pt, Pd and Rh surfaces due to their low hydrogenation and high CHx -OHy scission barriers, while deoxygenated linear products are favoured on Fe and Ni surfaces due to their low CHx -OHy scission and moderate hydrogenation barriers. Bimetallic alloy catalysts were also screened for their potential HDO activity and PtFe catalysts were found to significantly lower the ring opening and deoxygenation barriers relative to the corresponding pure metals. The developed BEPs for monometallic surfaces can be extended to estimate the barriers on bimetallic surfaces for ring opening and ring hydrogenation reactions but fails to predict the barriers for open-ring activation reactions due to the change in transition state binding sites on the bimetallic surface. The obtained BEP and TSS relationships can be used to develop microkinetic models for facilitating accelerated catalyst discovery for HDO.

Effect of Ni, Mo and W on hydrothermal co-liquefaction of macroalgae and microalgae: Impact on bio-crude yield and composition

The co-hydrothermal liquefaction of macroalgae (Enteromorpha Clathrata) and microalgae (Chlorella Vulgaris) with metal catalyst was conducted at the temperature of 350 °C. Ni/MCM-41, Mo/MCM-41 and W/MCM-41 catalysts were used to investigate the role of catalyst on the bio-oil yield and composition distribution during hydrothermal liquefaction. the physicochemical properties of MCM-41, Ni/MCM-41, Mo/MCM-41, and W/MCM-41 were investigated by SEM, XRD, XPS, and NH3-TPD. These catalysts all reduced the production of bio-oil but improved the quality of bio-oil. The results of ultimate analysis showed that Ni/MCM-41 revealed high performance in hydrodeoxygenation and upgrading of bio-oil, and had the highest HHV. Mo/MCM-41 displayed an achievement in increasing the content of hydrocarbons (23.04%) and reducing the relative content of acid products in bio-oil. The W/MCM-41 had the most obvious effect on increasing the content of ester compounds and reducing the content of N-containing compounds in bio-oil.

Plasma-assisted hydrodeoxygenation of bio-oils

Amid the backdrop of ever-escalating energy demand, dwindling energy resources, and fossil fuels-led climate conundrums, the staggering amount of clean and renewable energy supply to feed the energy-hungry civilization is the need of the day. On this frontier, biofuels turn out to be the greener energy substitutes and the use of plasma in sustainable bioeconomy has garnered huge attention recently. Although there are several review articles on plasma-driven biomass valorization and plasma-free hydrodeoxygenation (HDO) of bio-oils, none of the previous reviews on plasma-assisted HDO has been reported yet. This, in turn, highlights the novelty of this approach presenting efficient and sustainable avenues to produce high-quality biofuel. To bridge this significant literature gap regarding the integration of two processes, this review sheds light on growing trends in plasma technology, succinctly highlights the synergistic benefits of plasma-assisted HDO, and summarizes its recent progress for the upgradation of bio-oils into bio-based chemicals and value-added bioproducts together with in-depth critical analysis and comparison between both non-catalytic and catalytic plasma-assisted HDO of bio-oils. Despite being a cutting-edge solution in the upscaling of bio-oils, a limited amount of work has so far been conducted employing this integrated approach that nevertheless provides new insights for further advancements.

Rational design of Ni-MoO3–x catalyst towards efficient hydrodeoxygenation of lignin-derived bio-oil into naphthenes

Design of a robust catalyst with high activity but the low cost for the hydrodeoxygenation (HDO) of bio-oils is of great importance to bring the biorefinery concept into reality. In this study, density functional theory (DFT) calculation was adopted to analyze the optimal location of Ni on MoO3–x containing oxygen vacancy, and the corresponding result demonstrated that metallic Ni cluster located at the neighborhood of oxygen vacancies would significantly evoke HDO activity. Enlightened by DFT results, NiMoO4 was first hydrothermally synthesized and then employed to fabricate Ni-MoO3–x catalyst via a low-temperature reduction, where Ni escaped from NiMoO4 and was reduced to its metallic state. Such an evolution of Ni species also induced the formation of oxygen vacancies around metallic Ni cluster. In the HDO of p-cresol, Ni-MoO3–x exhibited high activity with a complete conversion and a methylcyclohexane selectivity of 99.4% at 150 °C. Moreover, the catalyst showed good versatility in catalyzing HDO of diverse lignin-derived oxygenates and lignin oil. 2D HSQC NMR, gas chromatograph and elemental analysis of the lignin oil demonstrated the high deoxygenation efficiency and saturation of the benzene ring over Ni-MoO3–x. In the upgrading of crude lignin oil, the deoxygenation degree was up to 99%, and the overall carbon yield of the naphthenes was as high as 69.4%. Importantly, the structures and carbon numbers of the naphthene products are similar to jet fuel-range cycloalkanes, which are expected to have a high density that can be blended into jet fuel to raise the range (or payload) of airplanes. This work demonstrates the feasibility for improving the targeted catalytic reactivity by rational tailoring the catalyst structure under the guidance of theoretical analysis, and provides an energy-efficient route for the upgrading of lignin crude oil into valuable naphthenes.

Critical role of support crystal structures on highly selective hydrodeoxygenation of lignin-derived vanillin over Pd/ZrO2 catalysts

Hydrodeoxygenation (HDO) of bio-oils obtained by rapid pyrolysis of biomass into high value-added chemicals generally required harsh conditions. Herein, three kinds of mixed-phase ZrO2 supports (denoted as ZSX, X = 2–4) with different crystal structure proportions were prepared by one-pot hydrothermal synthesis method, and their performance on the properties of Pd/ZrO2 catalysts were investigated for vanillin HDO. Pd/ZS3 exhibited excellent efficiency in HDO of vanillin, a typical model compound of lignin, achieving approximately 100% yield of 2-methoxy-4-methylphenol (MMP) in presence of n-butanol as solvent and polymethyl hydrogen siloxane (PMHS) as hydrogen donor under mild conditions (35 °C, 1 h). It was due to catalytic synergy of exposed metal active sites, oxygen vacancies (Ov) and acid sites to occur electron transfer and enhance interaction between Pd and ZrO2. By tuning the crystal structure of ZrO2 support, the influence of Ov and acid sites of Pd/ZrO2 over vanillin HDO performance was investigated, Pd/ZS2 with abundant Ov and Pd/ZS4 with substantial acid sites promoted hydrogenation and hydrogenolysis, respectively, Pd/ZS3 possessed preferable conversion and selectivity as having the properties of both at once. Additionally, reaction pathway was also proposed in which vanillin was converted to MMP by combining intermediate of 4-hydroxy-methyl-2-methoxyphenol (HMP) with active hydrogen species while removing water. This developed catalysts with different crystalline highlighted an enormous promise for HDO of bio-oils into green fuel under mild conditions.

Dynamics-driven tailoring of sub-nanometric Pt-Ni bimetals confined in hierarchical zeolite for catalytic hydrodeoxygenation

Metal-zeolite catalysts are promising for hydrodeoxygenation of bio-oils, but they always encounter sluggish diffusion kinetics due to sole micropores and inferior metal stability. Here, highly stable sub-nanoscale Pt-Ni bimetals confined in a hierarchical ZSM-5 zeolite (Pt-Ni@HZ) are constructed. The formed Pt-Ni@HZ species create framework-bonding metal sites with zeolite in a confined microenvironment, thereby establishing strong interactions and generating uniform distribution of Pt-Ni bimetals. In the Pt-Ni@HZ-catalyzed hydrodeoxygenation of phenolics, sub-nanometric Pt-Ni facilitates the adsorption and transfer of hydrogen, and hierarchical pores promote the diffusion kinetics of reactants. The designed Pt-Ni@HZ with small metal particles and high coordination numbers of Pt-Ni bonds, favors the complete deoxygenation of phenolics, with a higher yield of cyclohexane than conventional catalysts prepared by impregnation. Benefiting from the protection of the zeolite framework, the Pt-Ni@HZ catalyst exhibits high thermal stability and low leaching of metal active sites, with only 4.4 % catalyst deactivation after five reaction cycles.

The in-situ formation of supported hydrous ruthenium oxide in aqueous phase during HDO of lignin-derived fractions

The in-situ formation of supported hydrous ruthenium oxide (HRO) from RuO2 over micro-mesoporous materials is reported for the selective hydrogenation of bio-oil under mild reaction conditions (200 °C, 20 bar H2) in an aqueous medium. For the first time, the phase composition of HRO was determined using a variety of characterization techniques. Using synchrotron radiation and in-situ X-ray absorption spectroscopy (XAS), we demonstrated that HRO was generated during the hydrodeoxygenation process. The hydrodeoxygenation (HDO) of real bio-oil was successfully performed at 200 °C, 20 bar H2 on RuO2-containing catalysts. The approximate composition of HRO after 3 h of catalytic hydrogenation, consisted of in approximately equal ratios metallic Ru, RuO2, and RuOOH phases.