Phosphorus and Nitrogen Dual-Doped Few-Layered Porous Graphene: A High-Performance Anode Material for Lithium-Ion Batteries

Few-layered graphene networks composed of phosphorus and nitrogen dual-doped porous graphene (PNG) are synthesized via a MgO-templated chemical vapor deposition (CVD) using (NH₄)₃PO₄ as N and P source. P and N atoms have been substitutionally doped in graphene networks since the doping takes place at the same time with the graphene growth in the CVD process. Raman spectra show that the amount of defects or disorders increases after P and N atoms are incorporated into graphene frameworks. The doping levels of P and N measured by X-ray photoelectron spectroscopy are 0.6 and 2.6 at %, respectively. As anodes for Li ion batteries (LIBs), the PNG electrode exhibits high reversible capacity (2250 mA h g^–1 at the current density of 50 mA g^–1), excellent rate capability (750 mA h g^–1 at 1000 mA g^–1), and satisfactory cycling stability (no capacity decay after 1500 cycles), showing much enhanced electrode performance as compared to the undoped few-layered porous graphene. Our results show that the PNG is a promising candidate for anode materials in high-rate LIBs

Compositional Changes during Hydrodeoxygenation of Biomass Pyrolysis Oil

Hydrodeoxygenation (HDO) is usually considered as a promising process for upgrading biomass pyrolysis oil (PO) to bio-fuels. However, cognition of HDO is inhibited by the complexity of the PO and upgraded products. In this study, a PO and its upgraded pyrolysis oil (UPO) samples were analyzed by nuclear magnetic resonance, gas chromatography/mass spectrometry, and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). ESI FT-ICR MS revealed the most abundant compounds in PO were O₂–O₁₈ species with double bond equivalent (DBE) values of 0–22. After HDO, oxygen numbers gradually shifted to a range of O₁–O₁₀, and DBE number also progressively decreased. The major oxygen compounds such as carbonyls, carboxylic acids, ethers, carbohydrates, and alcohols were significantly changed with respect to relative content and molecular composition. Lignin polymers were depolymerized after reduction of the carbonyl and methoxy groups. For HDO, hydrogenation of carbonyls, carbohydrates, and furans occurred under 150 °C. Dehydration, hydrodeoxygenation, and dehydration–hydrogenation reactions were initiated at 210 °C. Decarboxylation and decarbonylation required higher temperatures (>300 °C)

Computational Investigation of a Turbulent Fluidized-bed FCC Regenerator

This paper presents a CFD modeling of hydrodynamics, heat transfer, and coke combustion in an industrial turbulent fluidized-bed FCC regenerator. Based on the Eulerian-Eulerian model, a CFD model including heat transfer and coke combustion reactions is established. The detailed hydrodynamics, temperature, and species concentration distribution inside the regenerator are obtained under various operating conditions. The flow behavior in the regenerator shows more turbulent disorder, causing the axial and radial nonuniformity of catalyst content, temperature, and species concentration. Increasing operating pressure and superficial gas velocity accelerates the coke combustion, leading to a higher combustion efficiency. However, the increases in initial coke content and spent catalyst circulation rate deteriorate the regeneration performances. The simulated regenerator could not burn more coke at the current operating conditions because of its limited coke-burning capacity. Improving entrance configuration, enhancing gas-particle contact, and prolonging reaction time would benefit the coke combustion

Influence of Framework Protons on the Adsorption Sites of the Benzene/HY System

Monte Carlo (MC) simulations were performed to study the influence of framework protons on the adsorption sites of the benzene molecule in HY zeolite with different Si:Al ratios. Eleven types of adsorption sites were observed including five reported sites (H1, H2, U4, U4­(H1), and W) and six newfound sites (W­(2H1), U4­(2H1), H1­(H2), U4­(H1,H1), H1­(H2,H1), and U4­(H1,H1,H1)), which were “supersites” with more than one proton. The stability order of the sites found in the 28Al model can be expressed as U4­(H1,H1,H1) > U4­(H1) > H1­(H2,H1) > W­(2H1) > U4­(H1,H1) > H1­(H2) > H1 > H2 > U4 > U4­(2H1) > W. Increasing number of zeolite protons resulted in an increasing proportion of supersites, which enhanced adsorption energies of sites. For HY zeolite models containing different numbers of protons with the same ratio of H1:H2, the amount of the most stable adsorption sites containing H1 proton increased, while the amount of the most stable adsorption sites containing H2 decreased, with increasing number of protons

Unraveling the Adsorption Mechanism of Mono- and Diaromatics in Faujasite Zeolite

Monte Carlo simulations are performed to study the adsorption of aromatic molecules (toluene, styrene, <i>o</i>-xylene, <i>m</i>-xylene, <i>p</i>-xylene, 1,3,5-trimethylbenzene, and naphthalene) in all-silica faujasite (FAU) zeolite. For monoaromatics, a two-stage “ideal adsorption” and “insertion adsorption” mechanism is found by careful inspection of locations and distributions of the adsorbed toluene molecules. The validity of this mechanism is confirmed for all monoaromatics considered in the current study. Remarkably, the number of C atoms per unit cell corresponding to the inflection point of adsorbate loading (<i>C</i>_I‑P) is defined as a valid and convenient characterizing factor in the packing efficiency of monoaromatics in the FAU zeolite. For the case of naphthalene, a type of diaromatic, the three-stage mechanism is proposed, which consists of the first two stages and a third stage of “overideal adsorption”. The so-called overideal adsorption is labeled because the naphthalene molecules start to occupy the S site nonideally at loadings that approach saturation, leading to a more localized feature of the adsorbates. The explicit adsorption mechanism can be used to understand the loading dependence of isosteric adsorption heat for the aromatics concerned

Theoretical Investigation of Water Gas Shift Reaction Catalyzed by Iron Group Carbonyl Complexes M(CO)₅ (M = Fe, Ru, Os)

We have investigated the mechanism of M­(CO)₅ (M = Fe, Ru, Os) catalyzed water gas shift reaction (WGSR) by using density functional theory and ab initio calculations. Our calculation results indicate that the whole reaction cycle consists of six steps: <b>1</b> → <b>2</b> → <b>3</b> → <b>4</b> → <b>5</b> → <b>6</b> → <b>2</b>. In this stepwise mechanism the metals Fe, Ru, and Os behave generally in a similar way. However, crucial differences appear in steps <b>3</b> → <b>4</b> → <b>5</b> which involve dihydride M­(H)₂(CO)₃COOH^– (<b>4′</b>) and/or dihydrogen complex MH₂(CO)₃COOH^– (<b>4</b>). The stability of the dihydrogen complexes becomes weaker down the iron group. The dihydrogen complex <b>4_Fe</b> is only 11.1 kJ/mol less stable than its dihydride <b>4′_Fe</b> at the B3LYP/II­(f)++//B3LYP/II­(f) level. Due to very low energy barrier it is very easy to realize the transform from <b>4_Fe</b> to <b>4′_Fe</b> and vice versa, and thus for Fe there is no substantial difference to differentiate <b>4</b> and <b>4′</b> for the reaction cycle. The most possible key intermediate <b>4′_Ru</b> is 38.2 kJ/mol more stable than <b>4_Ru</b>. However, the barrier for the conversion <b>3_Ru</b> → <b>4′_Ru</b> is 23.8 kJ/mol higher than that for <b>3_Ru</b> → <b>4_Ru</b>. Additionally, <b>4′_Ru</b> has to go through <b>4_Ru</b> to complete dehydrogenation <b>4′_Ru</b> → <b>5_Ru</b>. The concerted mechanism <b>4′_Ru</b> → <b>6_Ru</b>, in which the CO group attacks ruthenium while H₂ dissociates, can be excluded. In contrast to Fe and Ru, the dihydrogen complex of Os is too unstable to exist at the level of theory. Moreover, we predict Fe and Ru species are more favorable than Os species for the WGSR, because the energy barriers for the <b>4</b> → <b>5</b> processes of Fe and Ru are only 38.9 and 16.2 kJ/mol, respectively, whereas 140.5 kJ/mol is calculated for the conversion <b>4′</b> → <b>5</b> of Os, which is significantly higher. In general, the calculations are in good agreement with available experimental data. We hope that our work will be beneficial to the development and design of the WGSR catalyst with high performance

Combined Hydrotreating and Fluid Catalytic Cracking Processing for the Conversion of Inferior Coker Gas Oil: Effect on Nitrogen Compounds and Condensed Aromatics

Inferior coker gas oil (ICGO) derived from Venezuelan vacuum residue delayed coking is difficult to process using fluid catalytic cracking (FCC) or hydrocracking (HDC). The high content of nitrogen and condensed aromatics leads to major coking and readily deactivates the acid catalyst. In this work, a sequence of hydrotreating (HDT) and FCC processing is used to effectively convert ICGO to a high-value light oil product. The results show a higher overall conversion and a significant increase in the yield of gasoline compared to FCC processing. Molecular level characterization of the nitrogen compounds and condensed aromatics before and after HDT confirms that the nitrogen content and the 2+-ring aromatic content decreased, whereas the single-ring aromatics increased. The nitrogen compounds were mainly N₁, N₁O₁, N₁O₂, and N₁S₁ class species in basic nitrogen and N₁, N₁O₁, N₁O₂, N₂, and N₂O₁ class species in non-basic nitrogen. Moreover, the double bond equivalent of these species shifted to lower values. The decrease in the nitrogen compounds with a high heteroatom content reduces coking on the FCC catalyst. Subsequently, FCC unit performance and conversion to light oil increased. Moreover, the decrease in the size of N₁ class compounds and the ease of their cracking following HDT improved the performance of the FCC unit. Partial saturation of condensed aromatics following HDT also made it easier to crack these compounds

Hydroconversion Behavior of Asphaltenes under Liquid-Phase Hydrogenation Conditions

To fully utilize deoiled end-cut (DOE) from selective asphaltene extraction process, Venezuela <i>n</i>-pentane DOE was subjected to hydroconversion in an autoclave reactor using tetralin as hydrogen donor. Venezuela DOE and its hydroconversion products were separated into gas, <i>n</i>-heptane maltenes (HM), <i>n</i>-heptane asphaltenes (HAs), and coke. The effects of reaction conditions including reaction temperature, solvent-to-feedstock (S/F) weight ratio, and reaction time on product distribution were investigated. High temperature, large S/F ratio, and long time benefited the generation of gas, HM, and coke to some extent. Under optimal conditions, over 50 wt % HAs in DOE was converted into HM fraction, with less than 3 wt % coke yield. The elemental compositions and molecular weights of HAs and HM, along with reaction time, were also analyzed. The hydrogen-to-carbon (H/C) ratio of HAs declined from 1.115 to 0.871, indicating that HAs underwent dehydrogenation and dealkylation reactions. However, the H/C ratio of HM initially increased from 1.405 to 1.548, showing that hydrogenation reaction occurred, and then decreased to 1.374 because of the cracking of HAs into HM and/or the secondary cracking of HM. The average molecular-weight decrease both for HAs and HM confirmed disaggregation and cracking reactions. The molecular composition and transformation of nitrogen and sulfur compounds before and after hydroconversion were determined by negative- and positive-ion electrospray ionization Fourier transform ion-cyclotron–resonance mass spectrometry, respectively. N₁, S₁, and O₂ classes were dominant in the feedstock. After hydroconversion, N₁ and S₂ compounds decreased in HAs, indicating that they were reactive species. N₁ compounds mainly cracked into small N₁ compounds and also condensed into N₂ compounds, while S₂ compounds generally decomposed into S₁ compounds

Dissolution and Absorption: A Molecular Mechanism of Mesopore Formation in Alkaline Treatment of Zeolite

With the aim to optimize alkaline treatment of zeolites to obtain hierarchical zeolites, dissolution and absorption mechanisms relevant to mesopore formation were investigated at an atomistic scale by density functional calculations. In the dissolution processes, dealumination is energetically more favorable than desilication, though both processes can occur. The dissolved Al species prefer to be absorbed back onto zeolite surfaces whereas the dissolved Si species tend to aggregate in solution. The dissolution process promotes but the absorption process hampers the mesopore formation, laying foundation for understanding the mesoporosity influenced by the variations of zeolite framework and solution