Selective catalytic hydrogenation of naphthalene to tetralin over a Ni-Mo/Al2O3 catalyst

Modification of Activated Carbon and Its Application in Selective Hydrogenation of Naphthalene

The MoS₂/ACx catalyst for hydrogenation of naphthalene to tetralin was prepared with untreated and modified activated carbon (ACx) as support and characterized by X-ray powder diffraction, Brunauer-Emmett-Teller, scanning electron microscopy, temperature-programmed desorption of ammonia, X-ray photoelectron spectroscopy, and scaning transmission electron microscopy. The results show that the modification of activated carbon by HNO₃ changes the physical and chemical properties of activated carbon (AC), which mainly increases the micropore surface area of AC from 1091 to 1209 m²/g, increases the micropore volume of AC from 0.444 to 0.487 cm³/g, increases the oxygen-containing functional groups of AC from 5.46 to 7.52, and increases the acidity of catalysts from 365.7 to 559.2 mmol/g. The modified catalyst showed good catalytic performance, and the appropriate HNO₃ concentration is very important for the modified of activated carbon. Among all the catalysts used in this study, the MoS₂/AC3 catalyst could achieve the highest yield of tetralin. It can be attributed to the moderate acidity of the catalyst, reducing the cracking of hydrogenation products. Also, the proper hydrogenation activity of MoS₂ and the appropriate increase of oxygen-containing functional groups on the surface of modified activated carbon are beneficial to the dispersion of active components on the support, increasing the yield of tetralin. The catalytic performance of MoS₂/AC3 is better than that of MoS₂/Al₂O₃ catalyst, and the two catalysts show different hydrogenation paths of naphthalene.

Recovering valuable metals from spent hydrodesulfurization catalyst via blank roasting and alkaline leaching

Spent hydrodesulfurization (HDS) catalysts, containing considerable amount of pollutants and metals including vanadium (V), molybdenum (Mo), aluminum (Al), and nickel (Ni), are considered as hazardous wastes which will result in not only ecosystem damage but also squandering resource. Herein, a process featuring blank roasting-alkaline leaching is proposed to recover spent HDS catalyst. During roasting, low-valence compounds convert to high-valence oxides which can be leached out by NaOH solution. Afterwards, leaching solution is subjected to crystallization to separate metals. The results show that for samples roasted at 650 °C, 97% V, 96% Mo, and 88% Al are leached out at optimal condition; for samples roasted at 1000 °C, selective leaching of 91% V and 96% Mo respectively, are realized, with negligible Al being dissolved. NiO is insoluble in strong alkali leaving in residue. The advantages of this process are that first, the leaching of V, Mo, and Al can be manipulated by controlling roasting conditions, providing flexible process design. Second, leaching solution can be fully recycled. Finally, mild leaching condition and clean separation of V, Mo, and Al is achieved, proving fundamental information for peer researches to facilitate their future research on the development of more efficient and cleaner technologies.

Comparative Study on the Hydrogenation of Naphthalene over Both Al2O3-Supported Pd and NiMo Catalysts against a Novel LDH-Derived Ni-MMO-Supported Mo Catalyst

Naphthalene hydrogenation was studied over a novel Ni-Al-layered double hydroxide-derived Mo-doped mixed metal oxide (Mo-MMO), contrasted against bifunctional NiMo/Al₂O₃, and Pd-doped Al₂O₃ catalysts, the latter of which with Pd loadings of 1, 2, and 5 wt %. Reaction rate constants were derived from a pseudo-first-order kinetic pathway describing a two-step hydrogenation pathway to tetralin (k ₁) and decalin (k ₂). The Mo-MMO catalyst achieved comparable reaction rates to Pd_2%/Al₂O₃ at double concentration. When using Pd_5%/Al₂O₃, tetralin hydrogenation was favored over naphthalene hydrogenation culminating in a k ₂ value of 0.224 compared to a k ₁ value of 0.069. Ni- and Mo-based catalysts produced the most significant cis-decalin production, with Mo-MMO culminating at a cis/trans ratio of 0.62 as well as providing enhanced activity in naphthalene hydrogenation compared to NiMo/Al₂O₃. Consequently, Mo-MMO presents an opportunity to generate more alkyl naphthenes in subsequent hydrodecyclization reactions and therefore a higher cetane number in transport fuels. This is contrasted by a preferential production of trans-decalin observed when using all of the Al₂O₃-supported Pd catalysts, as a result of octalin intermediate orientations on the catalyst surface as a function of the electronic properties of Pd catalysts.

Catalytic Conversion of a ≥ 200 °C Fraction Separated from Low-Temperature Coal Tar into Light Aromatic Hydrocarbons

A ≥ 200 °C fraction (CT200F) of low-temperature coal tar was prepared by a rotary film evaporator. The catalytic conversion experiments of CT200F and six model compounds were conducted on the pyrolysis gas chromatography-mass spectrometer. The yields of catalytic conversion products benzene, toluene, xylene, and naphthalene (BTXN) were analyzed by semi-quantitative analysis according to the chromatographic peak areas. Additionally, the possible formation pathways and mechanisms of the target products BTXN generated over different catalysts were investigated. The results show that the yield of aromatic hydrocarbons increases and the yield of acid compounds decreases during CT200F pyrolysis over ZSM-5, HY, USY, and β-zeolite compared with that of its non-catalytic pyrolysis, especially the yields of BTXN obtained over USY and β-zeolite increase by 128 and 108%, respectively. The pore structure of ZSM-5 is suitable to produce BTX, while the suitable acidity and pore structure of USY, HY, and β-zeolite are more beneficial for the selective preparation of naphthalene than that of ZSM-5. The conversion pathways of six model compounds into BTXN over zeolites were obtained, and the following conclusions can be drawn: The dehydroxylation effect of zeolites shows the order of ZSM-5 > HY > USY > β-zeolite. The catalytic effect of zeolites on the cracking and ring opening of PAHs in CT200F shows the order of β-zeolite > USY > HY > ZSM-5. The catalytic effect of catalysts on the cracking and aromatization of aliphatic compounds shows the order of ZSM-5 > β-zeolite > USY > HY. β-zeolite has an outstanding catalytic performance in the conversion of PAHs into naphthalene. ZSM-5 and HY can effectively remove phenolic hydroxyl groups in phenol and naphthol. During the catalytic conversion processes of the coal tar fraction and model compounds, the catalytic effect of the pore constructions of zeolites is more important than their acidities, which determines whether large molecules can enter and whether acid sites in non-micropores can be effectively utilized.

New Approach to Synthesis of Tetralin via Naphthalene Hydrogenation in Supercritical Conditions Using Polymer-Stabilized Pt Nanoparticles

Supercritical (SC) fluid technologies are well-established methods in modern green chemical synthesis. Using SC fluids as solvents instead of traditional liquids gives benefits of higher diffusivity and lower viscosity, which allows mass transfer intensification and, thus, an increased production rate of chemical transformations. Therefore, a conjugation of heterogeneous catalysis with SC media is a large step toward a green chemistry. Tetralin (TL) is an important hydrogen donor solvent used for biomass liquefaction. In industry, TL is obtained via catalytic hydrogenation of naphthalene (NL). Herein, for the first time we have demonstrated the NL hydrogenation with close to 100% selectivity to TL at almost full conversion in the SC hexane. The observed transformation rates in SC hexane were much higher allowing process intensification. The downstream processes can be also facilitated since hexane after depressurisation can be easily separated from the reaction products via simple rectification. The TL synthesis was studied in a batch reactor at variation of reaction temperature and overall pressure. For the first time for this process, low Pt-loaded (1 wt.%) nanoparticles stabilized within hyper-cross-linked aromatic polymer (HAP) were applied. The Pt/HAP catalyst was stable under reaction conditions (250 °C, 6 MPa) allowing its recovery and reuse.