Reduction of NO with methane over Fe/ZSM-5 catalysts

<正>The catalytic activity of Fe/ZSM-5 for the selective reduction of NO to N_2 with methane in the presence of excess O_2 was studied.Fe/ZSM-5 catalysts with various Fe loadings were prepared by impregnation method.It is well known that methane is inactive when Fe/ZSM-5 as the catalyst for the selective catalytic reduction(SCR) of NO with methane.However,this paper shows that when the content of Fe was about 0.5%,Fe/ZSM-5 showed higher catalytic activity and selectivity of methane,and put forward measurable activation for CH_4 is an important factor for the reaction of removal of NOx with CH_4.     

Hydrodechlorination of chlorophenols over Pt- and Co-containing ZSM-5 zeolite catalysts

Summary Some of the chlorinated organic compounds are widely used commercially because of their advantageous chemical/physical properties or being toxic to pestiferous living substances. We have prepared and applied monometallic Co-, Pt- and bimetallic Co,Pt-ZSM-5 zeolite catalysts for hydrotreating 2- and 4-chlorophenols in the temperature range of 300-400 oC using a fixed-bed laboratory reactor system equipped with a gas chromatograph for analysis. In the reaction over the Pt-containing catalyst high initial conversion can be observed, the compounds transform to cyclohexanone, however, the activity of the catalyst decreases even during the 2 h reaction time. In the presence of Co-ZSM-5, the main reaction is simple hydrodechlorination resulting in phenol as the main product, and this catalyst is stable, and the activity does not change. The bimetallic catalyst combines the advantages (and disadvantages) of the monometallic samples. The hydroconversion of chlorophenols resulted in the formation of cyclohexanone with high initial selectivity. However, because of the relatively short catalyst lifetime further optimization is necessary before practical application.</o:p>     

Synthesis of novel metal/bimetal nanoparticle-modified ZSM-5 zeolite nanocomposite catalysts and application on toluene methylation

Research on Chemical Intermediates - Synthesis of Ag, Ni, Cu metallic and Ag/Ni, Ag/Cu bimetallic nanoparticles (NPs) was carried out by using metal nitrate salts as precursors via an easy and...     

H2 adsorption on Fe/ZSM-5 zeolite: a theoretical approach

The hydrogen reduction of the red-ox Fe/ZSM-5 zeolite is an essential step for catalyst preparation. In this letter, various adsorption modes of the H(2) molecules on the Fe(III)/ZSM-5 zeolite were first explored by density functional theory, with their exact configurations provided. The adsorption energies revealed that the two configurations with Fe(III) at the sextet states are the main ones, consistent with the results of inelastic neutron scattering (INS) experiments. On such basis, the vibrational and orbital analyses were made, which will be valuable for the future studies on the Fe/ZSM-5 systems.     

Propane aromatization over Pt?Sn/ZSM-5 catalysts

Addition of Sn modifies the catalytic performance of Pt/ZSM-5. Total conversions decrease with increasing Sn/Pt ratio. Selectivity to aromatics is higher on the Pt–Sn samples. A Pt–Sn interaction has been confirmed by H₂ chemisorption and TPR experiments.

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Sn Pt/ZSM5. Sn/Pt . Pt–Sn. Pt–Sn H₂ .

     

Ga改性ZSM-5分子筛催化丙烷芳构化性能研究

用离子交换法制备Ga改性ZSM-5双功能催化剂,并结合XRD、SEM、BET、NH₃-TPD、Py-IR及ICP、XPS等多种技术进行表征,考察分子筛硅铝比(Si/Al)和催化剂氧化还原预处理条件对分子筛的酸性质、Ga物种的存在状态及其丙烷芳构化催化性能的影响。研究表明,硅铝比不仅可以改变分子筛的酸性,也会影响分子筛中非骨架Ga物种与分子筛表面的相互作用程度,进而影响含Ga分子筛的丙烷芳构化性能。在质量空速1.0 h^-1、反应温度550℃ 下,Si/Al比为30的Ga-HZSM-5分子筛丙烷转化率和芳烃收率最高。Ga物种的引入可以提高丙烷的转化率和芳烃的选择性,并抑制烷烃、烯烃的裂解。H₂还原处理,将分子筛表面Ga₂O₃还原为低价的Ga⁺和GaH⁺₂物种,促进了Ga物种向分子筛微孔迁移;还原-氧化处理后,Ga⁺和GaH⁺₂物种氧化成GaO⁺,占据分子筛孔道离子交换位,显著提高了催化剂的芳构化活性。     

Methane activation over zeolite catalysts: The methylation of benzene

The methylation of benzene with methane over ZSM-5 zeolite catalysts in a high pressure static reactor is shown to require oxygen as a reactant, implicating methanol as a key intermediate species. In the case of zeolite H-beta, methyl aromatics can be formed in the absence of oxygen, consistent with an earlier report that these products are formed from cracking of benzene over the acid zeolite.     

Effect of protonation on hydroconversion of n-dodecane over Ni/ZSM-5 catalysts

The amount and distribution of acid sites are responsible for both conversion and product distribution in hydroconversion of n-dodecane over Ni/ZSM-5 catalysts. Catalytic stability is also related to the protonation degree of the samples.

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, - Ni/ZSM-5. .

     

Methane conversion into aromatic hydrocarbons over Ag-Mo/ZSM-5 catalysts

Nonoxidative methane conversion into aromatic hydrocarbons over ZSM-5-type high-silica zeolites modified with nanosized powders of molybdenum (4.0 wt %) and silver (0.1–0.5 wt %) is reported. The acidic properties of the catalysts have been investigated by temperature-programmed ammonia desorption. The microstructure and composition of the Ag-Mo/ZSM-5 catalytic systems have been studied by high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The doping of the Mocontaining zeolite with silver enhances its activity and stability in nonoxidative methane conversion into aromatic hydrocarbons.     

Ru/ZSM-5催化葡萄糖选择性加氢制备山梨醇(英)

采用无有机模板剂一步法制备了Ru/ZSM-5催化剂,利用X射线衍射、N₂吸附-脱附、NH₃-程序升温脱附和CO₂-程序升温脱附、扫描电镜和透射电镜等方法对催化剂进行了表征.考察了反应温度、钌负载量和催化剂重复利用等因素对Ru/ZSM-5上葡萄糖加氢反应性能的影响,并与浸渍法制备的Ru/ZSM-5催化剂进行了对比.结果表明,与传统浸渍法相比,一步法制备的Ru/ZSM-5催化剂钌粒子具有更高的分散性和稳定性.在120℃和4 MPa的温和反应条件下,葡萄糖接近完全转化,山梨醇选择性高达99.2%,催化剂可重复利用5次,仍保持较高活性.     

Transient kinetic studies and microkinetic modeling of primary olefin formation from dimethyl ether over ZSM-5 catalysts

The formation of primary olefins from dimethyl ether (DME) was studied over ZSM-5 catalysts at 300°C using a novel step response methodology in a temporal analysis of products (TAP) reactor. For the first time, the TAP reactor framework was used to conduct single- and multiple-step response cycles of DME (balance argon) over a shallow bed with the continuous flow panel. Propylene is the major primary olefin and portrays an S-shaped profile with a preceding induction period when it is not observed in the gas phase. Methanol and water portray overshoot profiles due to their different rates of generation and consumption. DME effluent shows a rapid rise halfway to its steady-state value leading to a slow rise thereafter because of its high desorption rates followed by subsequent reactions involving DME in further steps during the induction period. To analyze the experimental data quantitatively, nine reaction schemes were compared, and kinetic parameters were obtained by solving a transient plug flow reactor model with coupled dispersion, convection, adsorption, desorption, and reaction steps. The methoxymethyl pathway involving dimethoxyethane and methyl propenyl ether gives the closest match to experimental data in agreement with recent density functional theory studies. Gaseous dispersion coefficients of ca. 10⁻⁹ m² s⁻¹ were obtained in the TAP reactor. The novel experimental data validated against the transient kinetic model suggests that after the formation of initial species, the bottleneck in propylene formation is the transformation of the initial C–C bond, that is dimethoxyethane formed initially from DME and methoxymethyl groups. DME adsorption on ZSM-5 catalyst generates surface methoxy groups, which further react with the feed to give methoxymethyl groups. These methoxymethyl groups are regenerated through a series of reactions involving intermediates such as dimethoxymethane and methyl propenyl ether before propylene formation.     

Cs/ZSM-35 分子筛催化甲缩醛和乙酸甲酯发生一步法羟醛缩合反应

丙烯酸及其酯是重要的化工原料, 广泛应用于涂料、粘结剂、纤维等领域, 目前工业上常采用丙烯两段氧化法进行制备. 然而该方法以石油基原料丙烯为源头, 采用 V/Mo/Bi 等金属催化剂, 不符合可持续发展理念, 且存在环境污染及氧气下产物易过度氧化等问题. 因此, 如何高效、安全、大规模工业化制备丙烯酸及其酯是研究者追求的目标. 以乙酸甲酯(MAc) 和甲醛为原料, 通过羟醛缩合一步制备丙烯酸及其酯是一条完全不同于丙烯氧化法的合成路径, 原料均可由煤基甲醇得到, 符合我国"富煤、贫油、少气"的基本能源结构, 且该方法碳原子利用率为 100%, 副产物仅为水, 属于绿色环保合成路径.羟醛缩合是典型的碳链增长反应, 可在酸性催化剂、碱性催化剂、以及酸碱双功能催化剂存在下发生. 碱性催化剂一般为负载型碱金属氧化物, 例如以 SiO2为载体的负载型 Na, K, Cs 氧化物催化剂等, 但都存在活性组分流失的问题, 进而导致催化剂的失活, 难以实现工业化. 酸碱双功能催化剂是目前研究的热点, 由于具有酸催化剂的高选择性和碱催化剂的高活性, 其反应性能要远优于单一酸性催化剂和单一碱性催化剂, 广大研究者对此进行了深入广泛的研究, 目前基本处于实验室阶段. 相对而言, 目前酸性催化剂上通过羟醛缩合反应制备丙烯酸及其酯的研究工作较少, 特别是以固体酸为催化剂进行乙酸甲酯和甲醛气固相反应研究非常少见.我们以甲缩醛为甲醛源, 创新性地采用固体硅铝分子筛为酸性催化剂, 催化甲缩醛 (DMM) 和 MAc 发生羟醛缩合反应来制备丙烯酸. 硅铝分子筛具有较高的活性, 可高效地催化羟醛缩合反应, 且由于分子筛催化剂具有很好的再生性能, 即使催化剂寿命较短, 也可采用流化床或移动床等反应器进行工业化, 因此存在良好的工业化前景. 为了进一步深入研究酸性位和碱性位各自对 DMM 和 MAc 羟醛缩合反应的影响, 本文以 HZSM-35 分子筛为载体, 采用浸渍法制备不同碱金属铯氧化物含量的催化剂, 利用氮气吸附/脱附方法和化学程序升温 (NH3-TPD) 方法对其孔结构和酸性质进行表征, 并进一步考察催化剂的性能. 结果表明, 微孔体积随着碱金属 Cs 负载量的增加而逐渐减小, 当 Cs 负载量增加至 10 wt% 时, 样品微孔体积从初始 0.105 cm3/g 降至 0.063 cm3/g. NH3-TPD 结果显示, 当 Cs 负载量为 1 wt%, 酸性催化剂载体上的强酸和弱酸活性位被大量碱性氧化物占据; 当负载量超过 5 wt% 时, 所有的酸性位均被覆盖. 随后考察负载不同碱金属含量分子筛的羟醛缩合反应性能, 发现碱金属氧化物的引入不利于羟醛缩合反应的进行, 这主要是由于作为甲醛源的 DMM 只有在酸中心上才能进行分解产生甲醛, 促使羟醛缩合反应顺利进行. 当采用 DMM 为甲醛源时, 体系中必须有酸性位存在. 同时得知, 分子筛 HZSM-35 中强酸和弱酸均是羟醛缩合反应的有效酸性位, 但强酸同时催化原料发生类甲醇制烯烃过程, 致使大量烃类副产物生成, 产生较重的积炭物种. 羟醛缩合反应在含有大量弱酸催化剂上 (如γ-Al2O3) 也可顺利进行, 且具有较高的活性和稳定性.     

Pyrolysis of n-pentane on ZSM-5 zeolite

Pyrolysis of n-pentane has been studied at the temperature range 653–753 K on ZSM-5 zeolite. High catalytic activity and selectivity of H-ZSM-5 zeolite was found. The yield of propane was about 80 wt. %. A mechanism of the process is proposed.

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H-ZSM-5 n- 653–153 . . 80%. n-.

     

聚集态的Fe氧化物在Fe/ZSM-5催化N_2O直接分解中的作用(英文)

研究了以离子交换法制备的Fe/ZSM-5上聚合态的Fe氧化物(FeOx)在催化N2O直接分解中的作用.Fe/ZSM-5催化剂利用600–900 ℃的高纯Ar处理,使催化剂中的FeOx发生聚合.利用一系列的表征手段(XRD,BET,DRIFTS,UV/vis-DRS,XAFS,N2O脉冲和O2-TPD)对催化剂进行了表征.结果发现,分子筛骨架外的FeOx在Fe/ZSM-5催化N2O分解中起重要作用;通过研究高温处理的Fe/ZSM-5催化剂中不同FeOx的比例与催化剂活性的关系,得到多核的FeOx是催化N2O分解的主要活性物种;并且,无定形态的FeOx中键长较长的Fe–O键((Fe–O)2)是参与反应的重要物种.     

Oxidative conversion of methane over MgO/ZSM-5 catalysts with different Si/Al ratios

It is found that the lower the Si/Al ratio of ZSM-5 in the catalytic system MgO/ZSM-5, the higher is the activity and selectivity in the reaction of oxidative conversion of methane. The catalytic properties reflect quite closely the basic properties of the samples, studied by means of temperature-programmed desorption of CO₂.     

Enhancement of alpha-oxygen formation and N2O decomposition on Fe/ZSM-5 catalysts by extraframework Al

The concentration of alpha-oxygen which can oxidize methane to methanol and benzene to phenol at RT, increases linearly with the amount of introduced extraframework Al on Fe/ZSM-5 catalysts prepared by solid-state exchange of FeCl3 and AlCl3 with H-ZSM-5.     

Active Sites in Fe/ZSM-5 Zeolite

Fe/ZSM-5 zeolite has shown great potential in the selective oxidations of hydrocarbons such as methane and benzene. The various competing active sites of Fe/ZSM-5 zeolite are reviewed, including the mono-iron, oxygen-bridged [Fe, X] (X = Fe, Al) and peroxide species; in addition, the influences of H₂ pretreatment are considered. For the mono-iron species, the H₂ molecules are chemisorbed on the Fe(III) sites via the η²-binding mode. Both high- and low-spin Fe(III) ions play an important role during the H₂ reduction process whereas the former predominates in the N₂O decomposition process. As the calculated energy barriers indicate, the Fe(III) ions are facile to be reduced by H₂ pretreatment and therefore the active site of the mono-iron species should be in the FeO(OH) form. Instead, the oxygen-bridged [Fe, X] and peroxide species remain stable by H₂ pretreatment. The suitable oxygen-bridged [Fe, X] structures are screened out by comparisons with the experimental data and energy considerations from computational aspects. The geometries are in good agreement with the experimental data; meanwhile, it provides sound explanations to the distribution of the iron valence states, the thermodynamic facilitation of the “alfa-oxygen” generation by the introduction of extra-lattice Al ions as well as the shift of the Fe–Fe distances from ca. 3.06 to 2.53 Å. The superoxide species exists in Fe/ZSM-5 zeolite but not with the presence of extra-lattice Al ions. As the temperature increases, it gradually converts into the peroxide species and probably is the precursor of the peroxide species, one of the competing active sites in Fe/ZSM-5 zeolite. The clarification of active sites lays a solid foundation on the understanding of the catalytic processes and improvement of the Fe/ZSM-5 catalyst, one of the promising candidates to meet the industry challenges.     

Catalytic transformation of copaiba (Copaifera officinalis) oil over zeolite ZSM-5

The oil extracted from the trunk of the copaiba tree (Copaifera officinalis) is composed of sesquiterpenes, C₁₅H₂₄, and a small amount (>7 %) of sesquiterpenols, C₁₅H₂₆O; these were identified from their Kováts indices and mass spectra. The use of zeolites in the catalytic transformation of this renewable source of hydrocarbons is of interest in the search for new chemicals and ecologically clean fuels. Oil samples from copaiba trees growing in Colombia's Oriental Plains were circulated over zeolite ZSM-5 in a continuous flow fixed-bed micro reactor at 225, 265, and 325°C, for 1 h and subsequently analyzed by HRGC and GC-MS. Whereas only thirty four sesquiterpenes were identified in the original oil, over two hundred compounds were found in the product of the treatment of copaiba oil with zeolite ZSM-5. This complex mixture of sesquiterpenes, light aromatic compounds, and indene and naphthalene derivatives resulted from reactions such as isomerization, hydrogenation, cracking, and dehydrogenation with and without cracking. The amount of cracking products and aromatic compounds increased with reactor temperature but decreased with catalyst aging.