Ring Hydrogen Research Articles

Selective hydrogenation of anisole over Pt/SBA-15 catalysts: Effect of Pt loading on catalytic efficiency

Abstract Pt catalysts (0.1–2 wt.% of platinum) supported on SBA-15 were used for the selective hydrogenation of the aromatic ring of anisole with the formation of cyclohexyl methyl ether product. The catalysts were characterized by N2 physisorption, UV–vis diffuse reflectance spectroscopy, powder X-ray diffraction, and scanning and transmission electron microscopies. The reaction progress and the impact of Pt loading in the catalysts were analyzed by gas chromatography. All the catalysts demonstrated high catalytic activity for the hydrogenation of anisole to cyclohexyl methyl ether (CME), reaching 90–98% anisole conversion at 6-h reaction time with near 90% selectivity to CME (280 °C, 6.9 MPa total pressure). An increase in the Pt content led to a slight decrease in the selectivity to CME due to its transformation to cyclohexane. 1%Pt/SBA-15 catalyst was tested in three repeated catalytic cycles showing high stability and preservation of Pt nanoparticle dispersion. Graphical abstract

Molecular Insight into Hydrodeoxygenation of Naphthols: Iridium-Catalyzed Ring Hydrogenation and Substrate-Catalyzed Dehydration

Molecular Insight into Hydrodeoxygenation of Naphthols: Iridium-Catalyzed Ring Hydrogenation and Substrate-Catalyzed Dehydration

Ni-Co nano-alloys confined by N-doped porous carbon overlayer to boost hydrodeoxygenation of 5-hydroxymethylfurfural

Ni-Co nano-alloys confined by in-situ formed N-doped porous carbon overlayer have been prepared through chelation of metal cations with citric acid and urea followed by carbonization for hydrodeoxygenation of 5-hydroxymethylfurfural (HMF) into 2, 5-dimethylfuran (DMF). The results indicated that the Ni-Co nano-alloys were formed and homogeneously distributed within the N-doped porous carbon overlayer. The electronic effect of the Ni-Co nano-alloys significantly boosted hydrodeoxygenation activity of the Co2Ni1@NC catalyst and simultaneously inhibited further hydrogenation and opening of furan ring. The N-doped porous carbon overlayer around Ni-Co nano-alloys not only facilitated to disperse and stable Ni-Co nano-alloys through strong metal-support interaction, but also protected the Ni-Co nano-alloys from aggregation. Therefore, the Co2Ni1@NC catalyst offered superior catalytic performance with the HMF conversion of 100 % and DMF selectivity of 93.0 %. Moreover, the Co2Ni1@NC catalyst displayed excellent stability without significant activity loss after five recycles due to the spatial confinement of N-doped carbon overlayer.

Intensifying Cyclopentanone Synthesis from Furfural Using Supported Copper Catalysts.

This work addresses catalytic strategies to intensify the synthesis of cyclopentanone, a bio-based platform chemical and a potential SAF precursor, via Cu-catalyzed furfural hydrogenation in aqueous media. When performed in a single step, using either uniform or staged catalytic bed configuration, high temperature and hydrogen pressures (180 °C and 38 bar) are necessary for maximum CPO yields (37 and 49 %, respectively). Parallel furanic ring hydrogenation of furfural and polymerisation of intermediates, namely furfuryl alcohol (FFA), limit CPO yields. Employing a two step configuration with optimal catalyst bed can curb this limitation. First, the furanic ring hydrogenation can be suppressed by using milder conditions (i. e., 150 °C and 7 bar, and 14 seconds of residence time). Second, FFA hydrogenation using tandem catalysis, i. e., a mix of β-zeolite and Cu/ZrO2, at 180 °C, 38 bar and 0.6, allows sufficient time for CPO formation and minimises polymerisation of FFA, thereby resulting in 60 % CPO yield. Therefore, this work recommends a split strategy to produce CPO from furfural. Such modularity may aid in addressing flexible market needs.

The Reaction Mechanism and Rates at Ru Single-Atom Catalysts for Hydrogenation of Biomass BHMF to Produce BHMTHF for Renewable Polymers.

Realizing high selectivity for producing biodegradable 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) for renewable polymers from 5-hydroxymethylfurfural (HMF) biomass through ring hydrogenation on single-atom catalysts poses a considerable challenge due to the complexity of HMF functional groups and the difficulty of H2 dissociation. We developed a detailed reaction mechanism based on ab initio molecular dynamics (AIMD) and quantum mechanics (QM) to find that Ru single-atom catalysts can simultaneously dissociate H2 and perform the ring hydrogenation of biomass-derived 2,5-bis(hydroxymethyl)furan (BHMF) to produce biodegradable BHMTHF, with a free energy barrier of 0.82 eV. The unique property of Ru single-atom sites enables H2 to dissociate easily on a single active site of Ru to participate directly in the reaction without diffusion. Furthermore, our predicted reaction rate from microkinetic analysis indicates that ring hydrogenation and side-chain hydrogenolysis are much faster than ring-opening hydrogenation over the range of 300-550 K. The product BHMTHF dominates with a selectivity of 98.9% at 300 and 78.4% at 550 K (the second product is 5-methylfurfural (5-MFA)). This study underscores the unique effectiveness of Ru single atoms in ring hydrogenation reactions using H2 as the hydrogen source, offering insights for the design of single-atom catalysts for other biomass reactions.

Ru/TiO2 Catalyzed High‐Yield Synthesis of Furanic Diols by 5‐Hydroxymethylfurfural Hydrogenation with Switchable Selectivity

Abstract5‐Hydroxymethylfurfural (HMF) is a versatile platform molecule that can be derived from biomass feedstocks and catalytically converted into various value‐added chemicals. In this work, selective hydrogenation of HMF is investigated to produce valuable furan‐based diols, namely 2,5‐bis‐hydroxymethylfuran (BHMF) and 2,5‐bis‐hydroxymethyltetrahydrofuran (BHMTHF), using TiO2 supported Ru catalysts. The catalyst performance was fine‐tuned to achieve over 98% yield to BHMF and BHMTHF under optimized reaction conditions with very good recyclability. We pointed out several key factors allowing to maximize the yield towards the respective diols. Features such as the Ru nanoparticle size, the strength of metal‐support interactions and the presence of residual chlorine were found to significantly influence the reaction. A characteristic volcano‐shaped relationship was obtained between the particle size and the catalytic activity giving the highest diol yield for an optimum Ru nanoparticle size of 1.6 nm. Further, metal‐support interactions were found to be responsible for providing optimum Ru‐TiOx interfacial surface sites and chlorine was affecting the electronic properties of Ru nanoparticles, potentially benefiting to the selective formation of BHMF. The reaction time was shown to control the hydrogenation of the furan ring and the selectivity of the reaction, that can be directed optimally towards BHMF or BHMTHF.

Selective Hydrogenation of 5‐Hydroxymethylfurfural to 5‑Hydroxymethyltetrahydrofurfural Over Heterogeneous Pd Catalyst Under Mild Conditions

Abstract5‐Hydroxymethylfurfural (5‐HMF) derived from lignocellulose represents an important platform molecule that could be employed in the selective hydrogenation of the furan ring to prepare 5‑hydroxymethyltetrahydrofurfural (HMTHF). However, the reported catalytic systems for the synthesis of HMTHF using 5‐HMF still require additional hydrogen pressure. In this study, the Pd/ZrO2 catalyst with uniformly dispersed Pd nanoparticles was prepared via a simple impregnation reduction process. This catalyst exhibited excellent catalytic activity and selectivity for the hydrogenation of 5‐HMF to HMTHF. High HMTHF yields up to 92.3% were produced under mild reaction conditions of ambient hydrogen pressure and room temperature in methanol solvent. This result was superior to the most catalytic systems that had been reported so far. The mechanism study revealed that the active hydrogen species on the surface of the Pd nanoparticles and the reaction solvent in this study were the pivotal factors influencing the hydrogenation of furan rings in 5‐HMF.

Unveiling the effects of support crystal phase on Cu/Al2O3 catalysts for furfural selective hydrogenation to furfuryl alcohol

Support crystal phase plays a crucial role in the controlled CO hydrogenation over the supported catalysts. Herein, the effects of Al2O3 crystal phase (α, θ, η, and γ) on the supported Cu-based catalyst is highlighted for furfural (FAL) hydrogenation to furfuryl alcohol (FA). The evaluation results show that Cu/η-Al2O3 exhibits the best performance (FAL conversion: 99.7 %, FA selectivity: 94.0 %), highest TOF value (29.3 h−1) and lowest apparent activation energy (66.3 kJ/mol). The comprehensive characterizations unravel that Cu/η-Al2O3 has the smallest Cu nanoparticles and the highest content of Cu+ and Cu0, which facilitates H2 dissociation and FAL adsorption. The reaction mechanisms suggest that Cu/η-Al2O3 has the strongest FAL adsorption and FA desorption capacity. Moreover, it is demonstrated that FAL is linear chemical adsorption on the catalyst surface in the η1(O) configuration, which avoids the furan ring hydrogenation, and thereby, results in the high FA selectivity. This work would provide some references for developing the high-efficiency CO hydrogenation catalysts.

Selective switching hydrogenation products of 5-hydroxymethylfurfural at high substrate concentrations by regulating Pd-MgO interactions

Controlling the selective activation of one or some functional groups as desired is still a challenge in hydrogenation, especially at high substrate concentrations. Herein, Pd-MgO interfaces over Al2O3 were finely regulated for efficiently selective hydrogenation of furan ring in 5-hydroxymethylfurfural (HMF) to produce 5-hydroxymethyltetrahydro-2-furaldehyde (5-HMTHFF) or total hydrogenation to 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF), also inhibiting side reaction. The Pd-MgO/Al2O3 with 12.0 wt% of MgO selectively hydrogenates the furan rings with a 5-HMTHFF yield of 82.4 % while that with 2.0 wt% of MgO totally hydrogenates HMF with a DHMTHF yield of 96.2 % at high substrate concentrations (400 mM). Characterizations and DFT calculations demonstrated that oligomeric MgO species suppress the agglomeration of Pd nanoparticles and strengthen HMF adsorption, consequently promoting total hydrogenation. Furthermore, Pdδ+-MgO1-x sites between the crystallized MgO and Pd metal favored tilted adsorption on the interface and weakened the activation of the CO bond, consequently selectively producing 5-HMTHFF.

Computational insights into the deoxygenation reaction of biomass-derived phenolic compounds over Ni2P (001) catalysts

This research sets the scene for understanding the interaction of phenolic molecules (i.e., phenol, o-cresol, m-cresol, and p-cresol) with Ni2P catalyst surface and how their hydrodeoxygenation reaction progresses over the surface. The hydrodeoxygenation process is responsible for removing the oxygen content from the pyrolysis oil compounds, particularly through direct deoxygenation route. Ni2P, which is one of the most common transition metal phosphides, serves as a candidate surface of this study. Two main investigations were carried out including the optimization of (1) adsorption configuration of the phenolic compounds and the (2) net charge distribution between the surface and the adsorbate. According to the adsorption energy studies, the horizontal configuration of the o-cresol molecule on the Ni2P(001) hollow site presented the most optimized and stable configuration with the least negative adsorption energy (−0.26 eV), resulting in the most negative net charge density at −0.286 |e|, as determined by the Bader charge analysis. Upon adsorption on Ni2P(001) surface, o-cresol undergoes significant charge redistribution, where the oxygen atom (-OH group) exhibits a net charge of −1.3443 |e|, indicating electron transfer to the surface. The catalytic pathway proceeded with deoxygenation followed by ring hydrogenation to produce toluene (C7H8), such that C–O bond dissociation has a reaction energy of −0.715 eV, while C–H bond formation step had a reaction energy of 0.011 eV.

Biodegradation of 3-methylpyridine by an isolated strain, Gordonia rubripertincta ZJJ

Methylpyridines are a class of highly toxic pyridine derivatives. In this study, a novel degrading bacterium was isolated for 3-methylpyridine (3-MP) degradation (Gordonia rubripertincta ZJJ, GenBank accession NO. OP430847.1; CCTCC M 2022975). The maximum specific degradation rate, half-saturation constant and inhibition constant were fitted to be 0.48 h−1, 88.3 mg L−1 and 924.0 mg L−1, respectively. During 3-MP biodegradation, the lost total organic carbon was transformed into CO2 (67.4 %) and biomass (32.6 %), and ammonia nitrogen was almost the sole inorganic species with a conversion rate of 36.3 %. Three metabolic pathways were possibly involved in 3-MP degradation: I) methyl oxidation followed by ring hydroxylation and hydrogenation; II) rupture of C=C and C–N bonds after ring reduction; III) initial ring hydroxylation. The study not only provides a novel strain for the high-efficient degradation of 3-MP, but also contributes to an in-depth understanding of 3-MP biotransformation.

Unusually Large Ligand Field Splitting in Anionic Europium(III) Complexes Induced by a Small Imidazolic Counterion.

Luminescent trivalent lanthanide (Ln3+) complexes are compounds of technological interest due to their unique photophysical properties, particularly anionic tetrakis complexes, given their higher stability and emission quantum yields. However, structural studies on the cation-anion interaction in these complexes and the relation of such to luminescence are still lacking. Herein, the cation-anion interactions in two luminescent anionic tetrakis(2-thenoyltrifluoroacetonato)europate(III) complexes with alkylimidazolium cations, specifically 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium are investigated. The Eu3+ complexes were synthesized and characterized by elemental analysis, mass spectrometry, and single-crystal X-ray crystallography, and their luminescence spectra were recorded at 77 K. Quantum chemical calculations were also performed. X-ray crystallography revealed hydrogen bonds between the enolate ligands and imidazolium ring hydrogens. The 1-butyl-3-methylimidazolium complex had two crystallographic Eu3+ sites, also confirmed by luminescence spectroscopy. The 1-ethyl-3-methylimidazolium complex exhibited an unusual 300 cm-1 splitting in the 5D0 → 7F1 transition, as reproduced by ligand field calculations, suggesting a stronger hydrogen bonding due to the smaller substituent. We hypothesize that this strong bonding likely causes angular distortions, resulting in high ligand field splittings.

Selective hydroconversion of ethanolyzed soluble portion from the ethanolysis of Hanglaiwan long flame coal extraction residue over highly active Ni/SAPO-34 catalyst

The ethanolyzed soluble portion (SPE) prepared from the ethanolysis of Hanglaiwan long flame coal (HLFC) extraction residue was converted to catalytically hydroconverted SPE (CHSPE) by the catalytic hydroconversion (CHC) over Ni10 %/SAPO-34 at 200 °C under an initial hydrogen pressure of 5 MPa for 24 h. The possible mechanisms for the origin and synergic effect of active hydrogen had been speculated according to the reactions of HLFC-related model compounds. H2 can be activated by Ni10 %/SAPO-34 to produce H···H, H+, and H-, the synergic effect of which leads to cleaving >C-O- bonds. After the CHC, arenes and heteroatom-containing aromatic compounds in SPE are converted to cyclanes, indicating that aromatic ring hydrogenation and heteroatom removal occur simultaneously during the CHC of SPE. The relative abundance (RA) of CH-containing species in CHSPE is larger than that in SPE, while the RAs of oxygen- and nitrogen-containing species in CHSPE are smaller than those in SPE. In addition, Ni10 %/SAPO-34 has excellent cyclability for the CHC of SPE, and the relative content of cyclanes decreases only by 17.4 % after five recycles. Undoubtedly, this investigation provides an effective strategy for directional upgrading of derived soluble portion from low metamorphic coals.

Construction of Ni−Re Supported on Hydrotalcite‐Derived MgAl Catalysts for Promoting the Ring Hydrogenation of Furfural into Tetrahydrofurfuryl Alcohol in Water

AbstractBiomass‐derived feedstocks play a vital role in sustainable economies for renewable energy, waste management, energy security, and commercial prospects. This study focused on promoting the ring hydrogenation of furfural (FAL) into tetrahydrofurfuryl alcohol (THFA) in an aqueous solution using a potential Ni−Re‐supported hydrotalcite‐derived MgAl catalyst at different Ni : Re molar ratios. Structural analyses, such as an in situ time‐resolved X‐ray absorption near edge structure, under H2 reduction elucidated the simultaneous transformation of Re6+ and Re7+ to Re0 with the remaining highly stable Ni2+. The construction of Ni−Re on hydrotalcite‐derived MgAl catalyst resulted in the alleviated H2 reduction behavior, facilitated H2 adsorption and desorption processes, and suitable catalyst acidity detected by H2 temperature‐programmed reduction, and H2 and NH3 temperature‐programmed desorption experiments, respectively. Under optimized conditions, a maximum THFA yield of 78 % with a complete FAL conversion was attained using Ni1Re0.16/MgO−Al2O3 catalyst at a reaction temperature of 140 °C, H2 pressure of 20 bar, catalyst loading of 20 %, and reaction time of 2 h in a H2O system. Isotopic deuterium (D2O) labeling revealed that D substitution was notably pronounced through isotopic exchange between the D atom from D2O and H atom in FAL during its hydrogenation to THFA.

The synthesis of Ni-Co@NOMC and the regulation of its active sites for the selective conversion of furfural to cyclopentanone

Catalysts play a critical role in the selective conversion of furfural (FAL) in the aqueous-phase hydrogenation-rearrangement tandem reaction (AP-HRT). Herein, the N-doped bimetallic Ni-Co@NOMC was synthesized by solvent volatilization self-assembly method. The morphology and structure of the APF precursors were effectively controlled through adjustments in the synthesis and the presence of numerous pore channels and the substantial specific surface areas contributed to enhancing catalytic efficiency. Furthermore, this study also examined the synergistic interaction between the acid-base sites of the novel mesoporous N-doped carbon (NOMC) carrier and metal active sites to advance the succession of the furan ring hydrogenation and rearrangement processes. Specifically, the 99.9 % conversion of 8 wt% FAL solution was successfully accomplished with the 90.5 % selectivity of cyclopentanone catalyzed by 1.2-Ni-Co@NOMC catalysts. Therefore, this research holds significant importance for advancing the sustainable utilization of biomass resources in the future.

A solution for 4-propylguaiacol hydrodeoxygenation without ring saturation

We investigate solvent effects in the hydrodeoxygenation of 4-propylguaiacol (4PG, 166 amu), a key lignin-derived monomer, over Ru/C catalyst by combined operando synchrotron photoelectron photoion coincidence (PEPICO) spectroscopy and molecular dynamics simulations. With and without isooctane co-feeding, ring-hydrogenated 2-methoxy-4-propylcyclohexanol (172 amu) is the first product, due to the favorable flat adsorption configuration of 4PG on the catalyst surface. In contrast, tetrahydrofuran (THF)—a polar aprotic solvent that is representative of those used for lignin solubilization and upgrading—strongly coordinates to the catalyst surface at the oxygen atom. This induces a local steric hindrance, blocking the flat adsorption of 4PG more effectively, as it needs more Ru sites than the tilted adsorption configuration revealed by molecular dynamics simulations. Therefore, THF suppresses benzene ring hydrogenation, favoring a demethoxylation route that yields 4-propylphenol (136 amu), followed by dehydroxylation to propylbenzene (120 amu). Solvent selection may provide new avenues for controlling catalytic selectivity.

Influence of Ga doped CoMo/Al2O3 catalysts on the selective hydrogenation performance of polycyclic aromatic hydrocarbons

It is a challenge to effectively control the intermediate ring hydrogenation products in tricyclic aromatic hydrocracking reactions in order to further increase the selectivity of BTX. A series of doped gallium modified CoMo/Al2O3 catalysts were prepared, the effect of gallium on the catalyst's physicochemical properties, active phase structure and hydrogenation reaction pathway was studied. The study revealed that the doping of gallium species promoted the sulfidation of Mo species and improved the catalytic activity of the catalyst. The 1 % Ga-modified catalyst showed the best selective hydrogenation performance, in which the conversion rate of phenanthrene was up to 83.75 % and the selectivity for dihydrophenanthrene reached 28.60 %. In addition, DFT calculations show that the introduction of Ga into the active phase between the Co and Mo atoms results in a higher differential charge density in the middle ring, which is more conducive to hydrogen adsorption.

Hydrogenation of phenol to cyclohexanone catalyzed by isolated Pd cations in the micropores of zeolite

Cyclohexanone is a key raw material for manufacturing nylon and other chemicals. The sustainable conversion of biomass-derived phenol to cyclohexanone meets the requirements of sustainable development goal but still be challenging. Herein, a catalyst containing isolated Pd cations in zeolite, namely Pd1/ZSM-5, is investigated for the partial hydrogenation of phenol to cyclohexanone. Under 140 °C and 1.5 MPa of initial hydrogen pressure, the conversion of phenol reaches 95.6% with the selectivity to cyclohexanone of 99.9%. Besides, the turnover rate (TOR) of partial hydrogenation of phenol reaches 382.7 h−1. The mild adsorption affinity of cyclohexanone on catalytic sites leads to the high selectivity. Moreover, as unveiled by surface reactivity of phenol monitored by in-situ infrared spectrum, the oxygen atom of phenol hydroxyl group is adsorbed on the Brönsted acid site of Pd1/ZSM-5 as the key reaction step. The reaction intermediate involves the partial hydrogenation of benzene ring of phenol.

Catalytic Refining Lignin‐Derived Monomers: Seesaw Effect between Nanoparticle and Single‐Atom Pt

AbstractPt automatically adsorbed on oxygen vacancy of TiO2 via an in situ interfacial redox reaction, resulting in atomically dispersion of Pt on TiO2. In the upgrading of lignin‐derived 4‐propylguaiacol, single‐atom catalyst (SAC) Pt/TiO2−H achieved a conversion of 96.9 % and a demethoxylation selectivity of 93.3 % under 3 MPa H2 at 250 °C for 3 h, markedly different from the performance of nanoparticle counterpart that gave deep deoxygenation selectivity over 99.0 %. The high demethoxylation activity of SAC Pt/TiO2−H is mainly attributed to its weak hydrogen spillover capacity that suppressed the benzene ring hydrogenation and the deep deoxygenation. Additionally, SAC Pt/TiO2−H reduced the energy barrier of CAr−OCH3 bond cleavage and accordingly lowered the Gibbs free energy of the demethoxylation reaction. This facile method could fabricate single‐atom Au, Pd, Ir, and Ru supported on TiO2−H, demonstrating the generality of this strategy for the establishment of a library of SACs. Moreover, SAC exhibited versatile capacity in demethoxylation of different lignin‐derived monomers and high stability. This study showcases the superiority of atomically dispersed metal catalysts for selective demethoxylation reactions and proposes a renewable alternative to fossil‐based 4‐alkylphenols through upgrading of lignin‐derived monomers.

Catalytic Refining Lignin-Derived Monomers: Seesaw Effect between Nanoparticle and Single-Atom Pt.

Pt automatically adsorbed on oxygen vacancy of TiO2 via an in situ interfacial redox reaction, resulting in atomically dispersion of Pt on TiO2. In the upgrading of lignin-derived 4-propylguaiacol, single-atom catalyst (SAC) Pt/TiO2-H achieved a conversion of 96.9 % and a demethoxylation selectivity of 93.3 % under 3 MPa H2 at 250 °C for 3 h, markedly different from the performance of nanoparticle counterpart that gave deep deoxygenation selectivity over 99.0 %. The high demethoxylation activity of SAC Pt/TiO2-H is mainly attributed to its weak hydrogen spillover capacity that suppressed the benzene ring hydrogenation and the deep deoxygenation. Additionally, SAC Pt/TiO2-H reduced the energy barrier of CAr-OCH3 bond cleavage and accordingly lowered the Gibbs free energy of the demethoxylation reaction. This facile method could fabricate single-atom Au, Pd, Ir, and Ru supported on TiO2-H, demonstrating the generality of this strategy for the establishment of a library of SACs. Moreover, SAC exhibited versatile capacity in demethoxylation of different lignin-derived monomers and high stability. This study showcases the superiority of atomically dispersed metal catalysts for selective demethoxylation reactions and proposes a renewable alternative to fossil-based 4-alkylphenols through upgrading of lignin-derived monomers.