Hydrodesulfurization of Dibenzothiophene over MCM-41-Supported Pd and Pt Catalysts

Three series of aluminosilicate MCM-41 (Al-MCM-41) were synthesized using different aluminum sources, including aluminum isopropoxide (AlM-I), pseudoboehmite, and aluminum sulfate, by a hydrothermal method. The hydrodesulfurization (HDS) performance of the Al-MCM-41-supported Pd and Pt catalysts prepared with chlorided precursors were evaluated with dibenzothiophene (DBT) as the model sulfur-containing molecule, in comparison with those supported on a siliceous MCM-41 (SiM). Pd/SiM and Pt/SiM were not promising for DBT HDS because of their relatively low activities and the rapid irreversible deactivation. Pd and Pt supported on the acidic Al-MCM-41 materials showed higher dispersion and enhanced HDS performances. AlM-I, which possessed the strongest acidity, was the most promising among the mesoporous materials investigated. The deactivated Pd/AlM-I and Pt/AlM-I can be reversibly regenerated by H₂ reduction. DBT HDS over the Pd catalysts predominantly took the hydrogenation (HYD) pathway, whereas the direct desulfurization (DDS) pathway and HYD pathway were comparable for the Pt catalysts. Increasing the support acidity had no positive effect on the DDS activity of Pd but significantly enhanced its HYD activity, while the increase in the rate constant of DDS pathway was close to that of the HYD pathway for Al-MCM-41-supported Pt catalysts. The effect of the acid properties of the supports on the HDS performance of Pd and Pt catalysts was discussed by considering the formation of “electronic-deficient” particles and the hydrogen spillover process

Synthesis of Co-Doped Tungsten Phosphide Nanoparticles Supported on Carbon Supports as High-Efficiency HER Catalysts

Tungsten phosphide (WP) is believed to be a promising electrocatalyst in the electrochemical hydrogen evolution reaction (HER) for its unique catalytic performances. Nevertheless, its further application is severely limited by the agglomeration caused by the high preparation temperature (over 600 °C). Herein, we adopt a citric acid-guided two-stage aging method to prepare Co-doped WP with small particle size and higher dispersity on the surface of seven different carbon supports. Co is successfully incorporated into the lattice of WP, causing preferable catalytic performance. The introduction of seven different carbon supports enhances electronic metal-supported interaction and proves this two-stage aging method universal. The as-derived CoWP-CA/KB (two-step aging) featured a low overpotential of 111 mV to achieve a current density of 10 mA cm–2, along with a desirable Tafel slope of 58 mV dec–1, outperforming most of the WP-based electrocatalysts. Besides, the electrode possesses excellent stability for 60 h without significant attenuation. Its remarkable performance results from its structure (delicate particle size, uniform dispersion, and large specific surface area) and its electrocatalytic properties (large electrochemically active surface area, excellent electrical conductivity, enhanced interfacial charge transfer kinetics, and high turnover frequency). This novel synthesis strategy will be pivotal for designing robust non-noble metal-based electrocatalysts with high HER activity and durability to meet the future keen demand for hydrogen

Nanocatalysts Derived from Copper Phyllosilicate for Selective Hydrogenation of Quinoline

1,2,3,4-Tetrahydroquinoline (py-THQ) is a vital intermediate that is used in the production of medicines, agricultural chemicals, and other fine chemicals and is synthesized through the selective hydrogenation of quinoline. In this work, copper phyllosilicate catalysts were prepared by four different synthesis methods: deposition precipitation, ammonia evaporation, a urea-assisted gel method, and hydrothermal treatment. It was found that the different synthesis strategies led to different actual loadings of copper in the precursors. The optimal catalyst showed a py-THQ selectivity of 99.9% at a full conversion of quinoline in ethanol at 100 °C and 3.0 MPa H2 for 2 h. The remarkable enhancement of the performance may be attributed to the small particle size, the coexistence of Cu0 and Cu+, and the strong interaction of copper phyllosilicate by the deposition precipitation preparation method. The characterization results showed that Cu0 and Cu+ were generated during the restoration process and were derived from CuO and layered copper phyllosilicates, respectively. Additionally, the ratio of Cu+/(Cu+ + Cu0) changed with the reduction temperature. The strategy of the catalyst design and synthesis developed in this work has potential applications in other nitrogen heterocyclic hydrogenation reactions

Efficient Ni₂P/SiO₂ Catalysts with Enhanced Performance for the Hydrogenation of 4,6-Dimethyldibenzothiophene and Phenanthrene

Highly dispersed Ni2P catalysts (Ni2P/SiO2-DPx) were prepared by reducing the passivation-free precursors, which were obtained through the phosphidation of nickel phyllosilicate with sodium hypophosphite. The strong metal–support interaction of nickel phyllosilicate and the mild phosphidation conditions prevented the agglomeration of Ni particles and resulted in a smaller Ni2P particle size. The superior catalytic performance of the as-prepared Ni2P/SiO2-DP catalysts was evaluated in hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene and the hydrogenation of phenanthrene, in comparison with Ni2P/SiO2-IM and CoMoS/γ-Al2O3 prepared from a conventional incipient wetness impregnation method. The passivation-free Ni-P/SiO2-DPx precursors showed great storage stability, and Ni2P/SiO2-DP derived from the stored Ni-P/SiO2-DP precursors exhibited negligible loss of HDS activity. This method provides a potential preparation strategy for the industrial applications of transition metal phosphides without the temperature-programmed reduction and the subsequent passivation process

Selective Hydrodeoxygenation of Furfural to 2‑Methylfuran over Silica-Supported MoP Catalysts under Mild Conditions

In the catalytic conversion of biomass-derived furfural to 2-methylfuran, a concerted combination of hydrogenation and hydrogenolysis is required. Highly dispersed MoP catalysts supported on SiO2 were prepared by incipient impregnation with the aid of citric acid and subsequent temperature-programmed hydrogen reduction. The prepared MoP/SiO2 exhibited a markedly high performance in the selective hydrodeoxygenation of furfural to 2-methylfuran. A full conversion of furfural with 96.3% selectivity to 2-methylfuran under mild reaction conditions (120 °C, 1.0 MPa, WHSV: 0.3 h–1) was obtained with over 20% MoP/SiO2 in a continuous fixed bed reactor. The oxophilicity of Mo species and surface acidity of MoP might enhance the adsorption of furfural and the subsequent cleavage of the C–O bond of the intermediate furfuryl alcohol, leading to considerably high selectivity to 2-methylfuran. The complexion of Mo species with citric acid improved the dispersion of MoP particles due to the controllable decomposition of the complex in the course of preparation. Although the activity of MoP/SiO2 decreased gradually with the reaction time in 50 h, it could be restored by in situ hydrogen reduction

Fabrication of a Monolith Reactor in a Copper Tube by Polymerization of Acetylene for Flow Catalysis

Continuous-flow processing is considered as a disruptive technology in the synthesis of active pharmaceutical ingredients and other fine chemicals. However, it remains extremely challenging to immobilize heterogeneous catalysts in the channels of microreactors in a facile and flexible manner. In the present investigation, a polymer monolith coiled copper reactor was fabricated by Cu-catalyzed polymerization of acetylene at atmospheric pressure in the temperature range of 290–370 °C. The polymerization yielded a cotton-like structure of carbonaceous fibers, which were able to assemble by themselves to form a monolith inside the copper tube. The characterization results revealed that unsaturated CC groups, which are favorable for post-surface modification, were present on the carbonaceous fibers. After air oxidation at 160 °C for 10 h, a fraction of the CC groups were converted to CO groups. By strong interaction with CO groups, Pd was immobilized in the polymer monolith by circulating an ethanol solution of palladium acetate through the copper tube. A 1000 mm-long monolith tube reactor with an inner diameter of 2 mm with a Pd loading of 1.15 wt % was fabricated and used in the continuous Suzuki–Miyaura coupling reaction. An ethanol–water (2:1 in volume) solution of iodobenzene (0.0125 M), phenylboronic acid (0.0188 M), and potassium carbonate (0.0250 M) was used as the feed, and the reaction took place at 100 °C and 1.0 MPa. The selectivity to biphenyl was kept at >99% with complete conversion of iodobenzene in a 100 h run

Fabrication of a Monolith Reactor in a Copper Tube by Polymerization of Acetylene for Flow Catalysis

Continuous-flow processing is considered as a disruptive technology in the synthesis of active pharmaceutical ingredients and other fine chemicals. However, it remains extremely challenging to immobilize heterogeneous catalysts in the channels of microreactors in a facile and flexible manner. In the present investigation, a polymer monolith coiled copper reactor was fabricated by Cu-catalyzed polymerization of acetylene at atmospheric pressure in the temperature range of 290–370 °C. The polymerization yielded a cotton-like structure of carbonaceous fibers, which were able to assemble by themselves to form a monolith inside the copper tube. The characterization results revealed that unsaturated CC groups, which are favorable for post-surface modification, were present on the carbonaceous fibers. After air oxidation at 160 °C for 10 h, a fraction of the CC groups were converted to CO groups. By strong interaction with CO groups, Pd was immobilized in the polymer monolith by circulating an ethanol solution of palladium acetate through the copper tube. A 1000 mm-long monolith tube reactor with an inner diameter of 2 mm with a Pd loading of 1.15 wt % was fabricated and used in the continuous Suzuki–Miyaura coupling reaction. An ethanol–water (2:1 in volume) solution of iodobenzene (0.0125 M), phenylboronic acid (0.0188 M), and potassium carbonate (0.0250 M) was used as the feed, and the reaction took place at 100 °C and 1.0 MPa. The selectivity to biphenyl was kept at >99% with complete conversion of iodobenzene in a 100 h run

Aqueous Phase Hydrodeoxygenation of Phenol over Ni₃P‑CePO₄ Catalysts

Unsupported Ni₃P-CePO₄ catalysts were prepared by coprecipitation, followed by drying, calcination, and temperature-programmed reduction. The prepared catalysts were characterized by XRD, N₂ adsorption–desorption, TEM, STEM-EDS elemental mapping, XPS, NH₃-TPD, FT-IR of adsorbed pyridine, and H₂-TPR. Their catalytic performances in hydrodeoxygenation (HDO) were investigated using an aqueous solution of phenol (5.0 wt %) as the feed. CePO₄ was generated in coprecipitation and stable in the subsequent drying, calcination, and temperature-programmed reduction (final temperature 500 °C). It is shown that the addition of CePO₄ resulted in enhanced HDO activity, and a maximum activity appeared at a Ce/Ni ratio of 0.3. The presence of CePO₄ improved the dispersion of Ni₃P significantly, leading to enhanced hydrogenation activity. CePO₄ served as the major dehydration sites as well because of its surface acidity (mainly Lewis acid). In addition, the kinetics of the aqueous phase HDO of phenol and cyclohexanol catalyzed by Ni₃P and by Ni₃P-CePO₄ with Ce/Ni ratio of 0.3 were investigated

Interwoven Molecular Chains Obtained by Ionic Self-Assembly of Two Iron(III) Porphyrins with Opposite and Mismatched Charges

We report ionic self-assembly of positively charged FeIII meso-tetra­(N-methyl-4-pyridyl) porphyrin (FeIIINMePyP) with negatively charged FeIII meso-tetra­(4-sulfonatophenyl) porphyrin (FeIIITPPS4), leading to the formation of flower-like nanostructures composed of unprecedented three-dimensional (3D) entangled chains of porphyrin dimers. Molecular dynamics (MD) simulations show that the 3D entanglement of porphyrin chains closely correlates to mismatched charges present in porphyrin dimers like [FeIII(H2O)2NMePyP]5+/[FeIII(H2O)2TPPS4]3– that requires extra interactions or entanglement with neighboring ones to achieve electric neutrality. Interestingly, the interwoven chains bring in excellent thermal stability as evidenced by well maintenance of the flower-like morphology after pyrolysis at 775 °C in argon, which is in good agreement of high-temperature MD simulations. Meanwhile, heat treatment of the flower-like porphyrin nanostructure leads to the formation of a non-noble metal electrocatalyst (NNME) with largely inherited morphology. This exemplifies a new approach by combining ionic self-assembly with subsequent pyrolysis for the synthesis of NNMEs with desired control over the morphology of template-free NNMEs that has rarely been achieved prior to this study. Furthermore, our electrocatalyst exhibits excellent activity and durability toward oxygen reduction reaction as well as much better methanol tolerance compared with commercial Pt/C in alkaline solutions