HZSM-5在线提质生物油及催化剂失活机理分析

对不同使用时间的HZSM-5分子筛在线催化提质制取的生物油进行理化特性和成分分析,从生物油品质角度对HZSM-5的催化性能进行评价;并采用TG、BET、XRD、SEM和TEM等方法对失活的HZSM-5催化剂进行表征分析,探讨了HZSM-5催化提质生物油的失活机理,并进行再生研究。研究表明,HZSM-5分子筛可转化生物油中的酸类、醛类和酮类等"非期望"有机物,生成较多"期望"有机物,如酚类和芳烃类物质,降低生物油的氧含量及酸性,提高生物油的热值;HZSM-5使用80 min后,生物油品质明显变差,催化剂活性明显降低;失活催化剂上沉积的焦炭主要呈纤维状,同时,还存在少量石墨状焦炭,焦炭总量达14.12%,且使用过程中催化剂的比表面积和孔容均下降,晶粒的团聚现象加剧,结晶度下降;在催化提质过程中,在孔道内生成的石墨状焦炭及在表面形成的纤维状焦炭大量覆盖活性位点,使得催化剂失活。经550℃再生后,催化剂可恢复催化性能。     

Si-tolerance of iron doped Pt/alumina catalyst in the total oxidation of VOC

Summary In the present study the effects of addition of iron on the catalytic activity and Si tolerability of Pt/g-Al₂O₃in the total oxidation of volatile organic compounds were investigated. Preliminary results showed that there is a noticeable improvement effect on Si-tolerance of catalyst, particularly for short term poison exposure. Bulk analysis of deposited silicon on the catalyst surface indicated that both Pt/g-Al₂O₃and iron-doped pellets had roughly the same silicone uptakes. Deactivation of catalyst was reversible and much faster for iron doped sample. The promoting effects of iron were related to its electronegativity and, to blocking of fewer Pt sites when iron is present at the surface of the catalyst.     

焦油催化裂化催化剂积炭失活的实验研究

对白云石、石灰石作用下生物质热解焦油催化裂化过程中的积炭失活问题进行了研究，考察了较长反应时间内催化剂积炭量和焦油转化率的变化情况。最长运行时间32 h，所得积炭质量分数为3%～15%，焦油转化率下降到70％左右。对不同来源焦油的生焦性、催化裂化反应条件等对积炭形成的影响作了考察，并从动力学角度对催化活性与积炭量之间的关系进行了分析，得到了单层积炭和多层积炭阶段线性和指数形式的关联式。     

Study on the deactivation and regeneration of the ZSM-5 catalyst used in methanol to olefins

ZSM-5 zeolite catalyst modified by a trace of metal cations shows high activity and high selectivity for the reaction of methanol to olefins (MTO), but it inclines to deactivate during the reaction. In this paper, the mechanism of the catalyst deactivation and the regeneration method were studied by X-ray diffraction (XRD), N2 adsorption-desorption, infrared spectra (IR), and infrared spectra coupled with NH3 molecular probes (IR-NH3). These characterizations indicated that coke formation was the main reason for the catalyst deactivation. To regenerate the deactivated catalyst, two methods, i.e., calcination and methanol leaching, were used. N2 adsorption-desorption, IR and IR-NH3 characteriza-tions showed that both methods can eliminate coke deposited on the catalyst and make the catalyst reactivated. XRD showed that the structure of the catalyst did not change after regeneration. Interestingly, the regenerated catalyst even showed better catalytic performance of the MTO reaction than the fresh one. Besides, the calcination regeneration can eliminate coke more completely, however, the methanol leaching method can be more easily carried out in situ in the reactor.     

磷酸和水蒸气联合改性的HZSM-5的物化表征及催化研究

研究了磷和水蒸气联合改性HZSM-5样品的物化和催化性能。XRD和IR研究表明，没有新的晶相出现。NH3-TPD研究样品的酸性表明，经过磷改性后的样品的酸量明显下降。经过水热处理的样品的BET比表面明显降低，这可能归因于磷物种和铝物种对孔道的堵塞。氮吸附－脱附等温线研究表明，等温线为I型和IV型的复合型，滞后环为H4型。联合改性样品的正庚烷裂化转化率高于仅仅由水蒸气改性样品的正庚烷裂化转化率，从而显示出磷物种对沸石分子筛高温水蒸气脱铝的抑制作用。     

Role of hydrogen in catalytic dehydrogenation: Film diffusion controlled deactivation

The function of hydrogen used as carrier gas in catalytic dehydrogenation is to increase the selectivity and stability of catalysts. It slows down catalyst deactivation by either inhibiting deposition of potential coke precursors or facilitating their desorption by rehydrogenation. This function, in gas-solid catalytic dehydrogenation appears to be interphase mass transfer controlled by increased hydrogen linear flow velocities decreasing the extent of deactivation. Besides, deactivation appears to progress through two regimes, an initial short term followed by a long term deactivation.     

Hierarchical ZSM‐5 Zeolites in Shape‐Selective Xylene Isomerization: Role of Mesoporosity and Acid Site Speciation

The isomerization of o‐xylene, a prototypical example of shape‐selective catalysis by zeolites, was investigated on hierarchical porous ZSM‐5. Extensive intracrystalline mesoporosity in ZSM‐5 was introduced by controlled silicon leaching with NaOH. In addition to the development of secondary porosity, the treatment also induced substantial aluminum redistribution, increasing the density of Lewis acid sites located at the external surface of the crystals. However, the strength of the remaining Brønsted sites was not changed. The mesoporous zeolite displayed a higher o‐xylene conversion than its parent, owing to the reduced diffusion limitations. However, the selectivity to p‐xylene decreased, and fast deactivation due to coking occurred. This is mainly due to the deleterious effect of acidity at the substantially increased external surface and near the pore mouths. A consecutive mild HCl washing of the hierarchical zeolite proved effective to increase the p‐xylene selectivity and reduce the deactivation rate. The HCl‐washed hierarchical ZSM‐5 displayed an approximately twofold increase in p‐xylene yield compared to the purely microporous zeolite. The reaction was followed by operando infrared spectroscopy to simultaneously monitor the catalytic performance and the buildup of carbonaceous deposits on the surface. Our results show that the interplay between activity, selectivity, and stability in modified zeolites can be optimized by relatively simple post‐synthesis treatments, such as base leaching (introduction of mesoporosity) and acid washing (surface acidity modification).     

裂化催化剂水热失活动力学及装置平衡活性模型

根据裂化催化剂水热失活过程伴随着超稳化过程的特点，确定了对应不同自抑制函数的催化剂水热失活动力学模型方程。利用裂化催化剂水热失活实验数据进行参数估值，建立了裂化催化剂水热失活动力学模型。统计检验结果表明，二级自抑制的一级水热失活模型能很好地模拟实验数据，是较理想的水热失活动力学模型。考虑工业装置中裂化催化剂呈全混流，建立了裂化催化剂平衡活性模型方程，并且装置平衡催化剂微反活性的模型计算值与实测值相当吻合。该模型的预测结果表明，随着再生器温度或催化剂藏量的提高，平衡剂的微反活性逐步降低；平衡剂微反活性随催化剂单耗的提高先快速提高，然后缓慢提高。     

SCR脱硝催化剂失活及其原因研究

以运行后的蜂窝型SCR（Selective catalytic reduction）催化剂和新鲜催化剂为研究对象。应用红外光谱、氮气吸脱附、X射线衍射、电镜扫描等手段对新鲜催化剂及运行后催化剂进行表征。结果表明,运行后催化剂表面官能团发生了变化,比表面积严重降低,载体（TiO₂）产生了型变,并且催化剂表面微粒出现了团聚现象。对运行后催化剂活性降低的原因进行了研究,结果表明,脱硝催化剂在运行过程中遭遇了突发性高温(如t> 650℃),导致活性出现劣化。此外,催化剂表面沉积物中水溶性离子及砷、磷等物质也对催化活性产生了影响。     

Comparative analysis of bias in the collection of airborne pollutants: Tests on major aromatic VOC using three types of sorbent-based methods

This study was undertaken to establish one of the most reliable sampling methods and to precisely evaluate the bias involved in the collection of airborne pollutant samples. For the purpose of our study, we investigated the performance of three different types of sampling techniques by measuring major aromatic volatile organic compounds (VOC) in outdoor air; the target analytes specifically include benzene, toluene, ethylbenzene, and xylene (commonly called BTEX). As the first step of our approach, we designed and developed a multi-channel sampling system consisting of a six-port mass flow controller (SJU-MFC) system. Because this system allowed the collection of up to six replicate samples, our measurement results were analyzed and screened statistically for the derivation of high-quality BTEX data. The feasibility of this sampling system was further tested through a comparison with concurrent measurement data sets obtained by two additional, but independent, sampling techniques: (1) automatic continuous sampler (ACS) and (2) on-line GC (O-GC) system. Based on the data sets collected concurrently by three different sampling methods, we attempted to evaluate the compatibility of sampling techniques. Although the results obtained by SJU-MFC system were not statistically different from those of the O-GC system, they were moderately distinguishable from those of ACS. Such patterns were seen consistently, when examined by correlation analysis. The overall results of our study thus generally point out that the compatibility of data sets, when the proper caution is taken, improve significantly among different sampling methodologies.     

热处理对HZSM-5结构、酸性及催化乙醇脱水反应性能的影响

对商用HZSM-5分子筛进行高温热处理,利用X射线衍射(XRD)、核磁共振波谱法(²⁷Al-MAS NMR)低温氮吸附、电感耦和等离子体放射光谱(ICP-AES)、氨-程序升温脱附(NH₃-TPD)和吡啶吸附傅里叶变换红外(FT-IR)光谱等技术对高温热处理改性前后样品进行了表征,并考察了高温热处理对分子筛的结构、酸性及催化乙醇脱水制乙烯反应性能的影响。结果表明,热处理改性后的HZSM-5分子筛发生骨架脱铝,B酸减少,L酸增多,孔容增大,出现新的介孔;适中的酸性位和复合型的介-微双孔道结构使其减少了反应中的副反应,乙烯的选择性得到提高,催化剂寿命显著提高。     

用于乙烯芳构化反应的Zn/HZSM-5催化剂失活机制研究

采用浸渍法制备了Zn负载量（质量分数）分别为1%、2%、3%的Zn/HZSM-5分子筛催化剂,通过XRD、N₂吸附-脱附、NH₃-TPD、Py-FTIR、XPS、TG-DTA等技术,系统考察Zn/HZSM-5分子筛在乙烯芳构化反应的失活机制。结果表明,积炭是催化剂失活的主要原因,HZSM-5中Zn的添加在较大程度上抑制了催化剂的积炭行为;低Zn含量时催化剂失活缓慢,但Zn含量较高时,由于催化剂比表面积和孔体积极剧下降,催化剂失活加剧。反应过程中,分子筛上Zn物种存在迁移和流失行为,迁移行为体现为催化剂表面Zn的富集和相对比例的变化;Zn流失速率在不同反应阶段保持恒定,但受到Zn含量的影响,Zn含量越高、流失速率越大。外表面ZnO是分子筛催化剂Zn流失的主要物种,且随Zn负载量升高变化趋势愈加明显,其含量与积炭速率存在一定关联。     

Comparative study of analytical methods for the determination of chromium in groundwater samples containing iron

Determination of chromium in groundwater samples containing iron may pose analytical problems due to sorption and fixation of chromium species onto Fe(III) hydroxides. Parks et al. (Water Res. 2004, 38, 2827) hypothesized that chromium species trapped inside Fe(III) hydroxides i.e. “fixed chromium” may not be soluble by HNO₃ digestion (APHA method 3030 B). In such cases, hydroxylamine digestion is required to release “fixed chromium”. To verify the hypothesis, we carried out this study on groundwater samples containing chromium and iron, using different methods of APHA and EPA. The results showed the presence of “fixed chromium”, ranged between 0.1 and 19.2 μg L^{− 1}, contributing 0.2 to 14.1% towards true total chromium. Digestion of samples with HNO₃ released Cr(III) bound to organic complexes, but not the “fixed chromium”. The hydroxylamine digestion released “fixed chromium”, but not the Cr(III) bound to organic complexes. Microwave digestion of samples with HNO₃ + HCl was effective for the release of both “fixed” and “Cr(III)-organic complexes”. Cr(III) was only adsorbed onto suspended matter, whereas Cr(VI), and Cr(III)-organic complexes were not adsorbed onto suspended matter due to their solubility. Sample pH, buffering capacity, and matrix have a significant influence on the adsorption and fixation of chromium species onto Fe(III) hydroxides.     

Catalytic activity of layered aluminosilicates for VOC oxidation in the presence of NOx

Raw and variously modified layered aluminosilicates have been used as catalysts in the reaction of ethanol oxidation both in the presence and absence of NO_x. In this study, we clearly showed that the conversion of VOC on the modified layered aluminosilicates decreases slightly in the presence of NO_x. However, the presence of NO_x in the reaction mixture did not affect the stability of the used catalysts. Only a small change of selectivity depending on the carrier type as well as on the way of modification was found.     

Increase of ambient formaldehyde in Beijing and its implication for VOC reactivity

Influencing atmospheric OH radical budget and tropospheric ozone production,ambient formaldehyde(HCHO) is one of the key oxygenated volatile organic compounds(OVOCs).We present the variations on formaldehyde column densities in summertime in Beijing retrieved from ozone monitoring instrument(OMI) between 2005 and 2011.Satellite columns of HCHO correlated well with available ground-based measurements despite some noticeable differences.The orthogonal distance regression(ODR) method was used to estimate the ratio between satellite columns and ground-level concentrations,whereas ordinary least squares(OLS) method was used to fit the trend of ambient formaldehyde.The formaldehyde concentrations derived from HCHO columns were in the range of 7-12 ppbv and steadily increased at an approximate rate of 0.64 ppbv/yr(7.8%at 2005 level) with an uncertainty of 51%.VOC reactivity quantified by means of OH loss rates showed increasing contribution from formaldehyde and acetaldehyde, rising from 35%in 2005 to 40%in 2010,and decreasing contribution from anthropogenic VOCs,dropping from 49%in 2005 to 40%in 2010.More attention should be paid to understanding the net feedback of increasing formaldehyde to ozone formation potential.     

Kinetic study of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al2O3 catalyst

The kinetics of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al₂O₃ catalyst were studied. Performance test runs were carried out in a fixed-bed integral reactor. Using a power-law rate expression for the surface reaction kinetics and independent law for deactivation kinetics, the experimental data were analyzed both by integral and a novel differential method of analysis and the results were compared. To avoid fluctuation of time-derivatives of conversion required for differential analysis, the conversion-time data were first fitted with appropriate functions. While the time-zero and rate constant of reaction were largely insensitive to the function employed, the rate constant of deactivation was much more sensitive to the function form. The advantage of the proposed differential method, however, is that the integration of the rate expression is not necessary which otherwise could be complicated or impossible. It was also found that the reaction is not limited by external and internal mass transfer limitations, implying that the employed kinetics could be considered as intrinsic ones.     

Unusual deactivation in the asymmetric hydrogenation of itaconic acid

The formation of unusual Rh(III) substrate complexes from [Rh(DIPAMP)(MeOH)₂]BF₄ and itaconic acid has been detected which leads to the deactivation of the catalyst. The influence of different parameters on the formation of such complexes, namely substrate concentration, reaction time, temperature, acidic and basic additives, was investigated with different NMR methods. Two different Rh(III) substrate complexes are formed whose ratio is strongly dependent on substrate concentration and reaction time. The pH value of the solution shows a strong influence on the chemical shifts of the ³¹P NMR signals of such complexes. A catalyst-mediated esterification of itaconic acid in methanol was detected. Extended investigations provide detailed ¹H, ¹³C and ³¹P NMR data for the Rh(III) complexes and information about their stability in solution.     

Studies on formation of carbonaceous deposits and catalytic deactivation of H-ZSM-5 zeolites

The rate of catalytic deactivation of H-ZSM-5 type zeolites and the nature of the resulting carbonaceous deposits have been studied in relation to zeolite Si/Al ratio, modifier content, and experimental reaction temperature.The conversion of 1-hexene carried out in a static cyclic system over a temperature range of 398–523 K has been used as a test reaction. The zeolites with higher aluminium content in the lattice have been found to exhibit not only enhanced activity over the initial period of operation but also slower deactivation and this in spite of the more intense carbon deposit buildup. The lower-temperature deposits are mostly saturated hydrocarbons in nature. As the zeolite Si/Al ratio is increased and reactant contact time protracted, the degree of carbonization of the deposit rises but only slightly. At elevated experimental reaction temperatures and particularly in the presence of water vapor, the effect is becoming increasingly pronounced.

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H-ZSM-5 Si/Al , . 1- 398–523 . à , , . . Si/Al , , . , .

     

Isolation of rhenium and ReOx species within ZSM5 channels and their catalytic function in the activation of alkanes and alkanols

Synthesis protocols, structures, and reactivity of Re-oxo species grafted onto H-ZSM5, and their subsequent conversion to Re-clusters through contact with H2 or CH4 were studied by using Raman, infrared, and X-ray absorption spectroscopies. Reactivity measurements by using alkane and alkanol reactants were also examined. Sublimation of Re(2)O(7) at 723 K led to a stoichiometric exchange with each ReO(x) species replacing one proton. Raman features for Re(2)O(7) disappeared during thermal treatment and Raman bands assigned to distorted-tetrahedral Si-O(f)ReO(3)-Al (O(f): zeolite-lattice oxygen atoms) species emerged; infrared bands for acidic OH groups in H-ZSM5 weakened concurrently. X-ray absorption near-edge and fine-structure spectra detected the formation of distorted-tetrahedral Re7+-oxo species during thermal treatment of Re(2)O(7)/H-ZSM5 mixtures in air, and their subsequent reduction to Re(0) in H2 or CH4 to form encapsulated Re metal clusters similar in diameter (approximately 8 A) to the channel intersections in ZSM5. Si-O(f)ReO(3)-Al species in ReO(x)-ZSM5 catalyzed the oxidative conversion of C(2)H(5)OH to acetaldehyde, acetal, and ethyl acetate with very low selectivity to CO(x) (<1 %). Unprecedented turnover rates were exhibited at temperatures much lower than previously found for ReO(x)-based catalysts, and without deactivation or sublimation processes ubiquitous in crystalline Re7+ compounds at temperatures required for catalysis. Encapsulated Re metal clusters formed by the reduction of Si-O(f)ReO(3)-Al precursors led to CH4 pyrolysis and C(3)H(8) dehydrocyclodimerization rates (per Re) that are higher than those previously reported for zeolite-based catalysts. The rate of CH4 conversion to benzene, by using Re-ZSM5, was approximately 30 % higher than that of the best reported catalysts, based on encapsulated MoC(x) clusters, whereas C(2)H(4) and C6+ arene selectivities were similar. C(3)H(8) activity and selectivity of Re-ZSM5 was significantly higher than that of Ga-ZSM5, the best reported catalyst for these reactions. Reaction rates (per Re) were independent of the Re/Al(f) (Al(f): aluminum framework) ratio for both Re and ReO(x) species. This is consistent with the uniform character of the structures formed during grafting of the ReO(x) species through sublimation and their ability to retain their homogeneity even after their reduction to encapsulated Re-clusters.