Controllable fabrication and catalytic activity of highly b‐oriented HZSM‐5 coatings

Multilayer b‐orientated HZSM‐5 catalytic coating is controllably synthesized by repeated growth of zeolite layer on Ti?OH‐modified surface of sublayer. The as‐prepared zeolite coating shows performance enhancement up to 110% in catalytic cracking of n‐dodecane ascribed to enhanced mass transfer in its straight and short pathway along the b‐axis. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1964–1968, 2014     

Preparation and Performances of Hierarchical Structured HZSM‐5 Washcoating on Stainless‐Steel Substrates

The washcoats of the hierarchical HZSM‐5 zeolite (through desilication) were prepared on the inner surface of SS304 stainless‐steel tubes. The properties of slurries and coatings were characterized by analysis of particle size, measurements of rheological property, loading, adhesion, and finally the catalytic cracking test. It was found that introducing mesoporosity on the zeolite crystals was beneficial for reducing the particle size during ball milling for slurries preparation, which was helpful for improving loading due to a significant change in the rheological property. As the interaction between the particles with different sizes was enhanced after ball milling, the adhesion of the prepared coatings was improved. The catalytic activity and stability of the hierarchical HZSM‐5 coatings for the catalytic cracking of n‐dodecane were 56% and 75% higher than that of the conventional one, respectively. This probably resulted from the enhanced diffusion rate of reactant and products in the crystals and the coatings.     

Effects of Colloidal Silica Binder on Catalytic Activity and Adhesion of HZSM-5 Coatings for Structured Reactors

HZSM-5 coating using three colloidal silica binders, acidic col oidal silica (ACS), neutral colloidal silica (NCS) and basic col oidal silica (BCS), was prepared to study the effect of binders on their...     

MAS NMR, ESR and TPD studies of Mo/HZSM‐5 catalysts: evidence for the migration of molybdenum species into the zeolitic channels

NH₃‐TPD, MAS NMR and ESR spectroscopies were employed to investigate Mo‐modified HZSM‐5 catalysts prepared by impregnation. It was found that the modification of Mo ions results in a pronounced decrease in the intensity of ¹H MAS NMR resonance originating from Brønsted acid sites in the zeolites and a distinct splitting of Mo⁵⁺ ESR signals, which is attributed to the interaction of Mo with the Al atom of the zeolite framework. This presents distinct evidence that Mo ions migrate from the external surface of the zeolite into the lattice channels during the impregnation and subsequent treatment. The remaining Brønsted acid sites associated with the migrated Mo ions form the bifunctional catalytic centers that may be responsible for the outstanding catalytic performance in methane aromatization.     

Catalytic Combustion‐Type Hydrogen Sensor Using BaTiO3‐based PTC Thermistor

A catalytic combustion‐type gas sensor using a positive temperature coefficient (PTC) thermistor, which shows a sharp resistance change around Curie temperature, was developed for the detection of hydrogen. La‐doped BaTiO₃ (Ba_0.998 La_0.002 TiO₃) was prepared through a solid‐state method and an oxalic acid method. La‐doped BaTiO₃ obtained by the oxalic acid method showed improved PTC properties, due to the formation of fine particles, as compared to that prepared with the solid‐state method. The resulting sensor device showed a fairly high H₂ sensitivity in the range of 100–1000 ppm. In addition, the H₂ sensitivity and response speed were improved by coating a Pt/SiO₂ catalyst on the sensor device because the catalytic combustion efficiency of H₂ was improved by the catalyst coating.     

Removal of methylene blue from aqueous solution by electrophoretically deposited titania‐halloysite nanotubes coatings

Two‐component suspensions of titania and halloysite nanotubes (HNTs) were prepared in ethanol with 0.5 g/L (optimum concentration) of polyethyleneimine (PEI) and different wt% of HNTs. Kinetics of Electrophoretic deposition (EPD) decreased with increasing the HNTs content in suspensions due to their less mobility compared with titania particles. HNTs reinforced the microstructure of coatings and reduced or completely prevented from cracking during drying and heat‐treatment steps. Removal of methylene blue (MB) via adsorption by HNTs coatings was faster than its photocatalytic degradation by titania coating. Dispersion of HNTs (up to ≈30 wt%) in the matrix of titania resulted in the synergistic catalytic effect in MB removal. The synergistic effect was because of the shorter traveling distance of MB molecules adsorbed on HNTs toward the photocatalytic active site of titania particles in composite coatings. However, the synergistic effect was destroyed with increasing the HNTs content in coating. Difference between the amount of MB removed by titania and composite coatings increased at longer times (≥60 minutes). Mass transfer of MB adsorbed on HNTs toward the photocatalytic active sites of adjacent titania particles can compensate the decline in the mass transfer from solution at longer times.     

芳烃精制脱烯烃分子筛催化剂的研究

本研究以铝胶、硅铝胶及钛铝胶为粘合剂,以HY分子筛为主要活性组分制备了芳烃脱烯烃分子筛催化剂.采用NH3-TPD、BET、TG和活性评价等方法对催化剂的酸性、脱烯烃活性、失活原因及再生性能进行了研究.结果表明,含有不同粘合剂的HY分子筛催化剂的脱烯烃活性均明显高于工业使用的NC-01颗粒白土催化剂,分子筛催化剂表面具有较多的弱酸中心是其性能良好的重要原因.积碳是分子筛催化剂表面失活的主要原因,经焙烧再生处理后分子筛催化剂仍具有较好的脱烯烃性能.经823 K焙烧的硅铝胶质量分数为20%的分子筛催化剂具有较佳的反应性能.     

Pyrolytic lignin removal for the valorization of biomass pyrolysis crude bio‐oil by catalytic transformation

BACKGROUND: The catalytic processes for valorizing the bio‐oil obtained from lignocellulosic biomass pyrolysis face the problem that a great amount of carbonaceous material is deposited on the catalyst due to the polymerization of phenol‐derived compounds in the crude bio‐oil. This carbonaceous material blocks the catalytic bed and contributes to rapid catalyst deactivation. This paper studies an on‐line two‐step process, in which the first one separates the polymerizable material and produces a reproducible material whose valorization is of commercial interest. RESULTS: The establishment of a step for pyrolytic lignin deposition at 400 °C avoids the blockage of the on‐line catalytic bed and attenuates the deactivation of a HZSM‐5 zeolite based catalyst used for hydrocarbon production. The origin of catalyst deactivation is coke deposition, which has two fractions (thermal and catalytic), whose content is attenuated by prior pyrolytic lignin separation and by co‐feeding methanol. The morphology and properties of the material deposited in the first step (pyrolytic lignin) are similar to lignins obtained as a by‐product in wood pulp manufacturing. CONCLUSIONS: The proposed reaction strategy, with two steps (thermal and catalytic) in series, valorizes the crude bio‐oil by solving the problems caused by the polymerization of phenolic compounds, which are obtained in the pyrolysis of the lignin contained in lignocellulosic biomass. Given that a by‐product (pyrolytic lignin) is obtained with similar properties to the lignin from wood pulping manufacturing, the perspectives for the viability of lignocellulosic biomass valorization are promising, which is essential for furthering its implementation in biorefinery processes. Copyright © 2009 Society of Chemical Industry     

Study of operating variables in the transformation of aqueous ethanol into hydrocarbons on an HZSM‐5 zeolite

With the aim of determining the possibilities of directly upgrading the liquid obtained from carbohydrate fermentation, the effect of operating conditions (temperature, space time, water content in the feed) has been studied in the catalytic transformation of aqueous ethanol into hydrocarbons on an HZSM‐5 zeolite in an isothermal fixed bed reactor. Special attention has been paid to the effect of water content on the yield, product distribution and catalyst deactivation. Although deactivation by coke decreases as the water content is increased, this content must be limited at 450 °C and higher temperatures in order to avoid irreversible deactivation of the catalyst by dealumination. © 2002 Society of Chemical Industry     

Acid Sites in HZSM‐5 Upon Copper Exchange by FTIR and DSC Using Ammonia

The acidity of the parent HZSM‐5 zeolite and Cu‐HZSM‐5 catalyst has been examined by FTIR and DSC using ammonia desorption. Sites of different strength were found in HZSM‐5, desorbing ammonia at a relative temperature difference of about 100 °C. Upon copper exchange a fraction of Brønsted sites were transformed to Lewis sites, but the acid strength of the remaining Brønsted sites was increased. Aside from Lewis sites originating from copper exchange, there might be some additional sites formed from precipitated copper. This could explain the quantity of adsorbed NH₃ on Cu‐ZSM‐5 which is higher than theoretically expected. While changing their nature, acid sites of higher strength keep their location, which is manifested by some diffusion effect towards ammonia.     

The effect of pretreatment procedures on the activities of Fe- and Mn-promoted sulfated zirconia catalysts

The vapour phase acylation of furan and pyrrole was carried out over HZSM‐5(19.7), HZSM‐5(30), HZSM‐5(280), CeHZSM‐5(30), LaHZSM‐5(30), HY and CeHY zeolites in a fixed bed reactor at atmospheric pressure using acetic anhydride as an acylating agent. The catalytic activity of the zeolite catalysts was dependent on the reaction temperature and the type of cation promoter used in the modification of the zeolite surface. The activity of the catalysts varied with the acidity of the zeloite systems tested. The yields of 2‐acetylfuran and 2‐acetylpyrrole with respect to the conversion of furan and pyrrole were 67.5% and 75.5% respectively. The acylation was found to be more active on Brønsted acidic sites available over zeolite systems.     

Converting Alkali Lignin to Biofuels over NiO/HZSM‐5 Catalysts Using a Two‐Stage Reactor

A series of NiO/HZSM‐5 catalysts were used to convert alkali lignin to hydrocarbon biofuels in a two‐stage catalytic pyrolysis system. The results indicated that all NiO/HZSM‐5 catalysts reduced the content of undesirable phenols, furans, and alcohols of the biofuel compared to non‐catalytic treatment. The NiO/HZSM‐5 catalyst with the lowest amount of NiO generated the highest biofuel yield in all catalytic treatments, and it also produced biofuel with the highest content of hydrocarbons. The emission of carbon oxides (CO and CO₂) increased in the treatments with higher‐NiO loading HZSM‐5 due to the redox reaction between NiO and the oxygenated compounds in the bio‐oil. Ni₂SiO₄ was generated in the used NiO/HZSM‐5 catalysts during the high‐temperature pyrolysis process.     

Influence of alumina binders on adhesion and cohesion during preparation of Cu‐SAPO‐34/monolith catalysts

The adhesion and cohesion between the coating layers and the ceramic honeycombs are usually one of the key issues in the preparation of high‐performance zeolite‐based/Monolith catalysts. In this work, we investigate the deposition of high‐efficiency Cu‐SAPO‐34 catalyst on a cordierite monolith with special focus on the impact of alumina binders on the structure, mechanical adhesion and cohesion, and catalytic performance of the monolithic catalyst. Two kinds of alumina nanoparticles, α‐alumina and γ‐alumina, have no significant impacts on the Cu‐SAPO‐34 crystal structure, micropore morphology and catalytic activity. But washcoating experiments showed that the mass loss rate of the coating was less and the loading of the catalyst was higher when α‐alumina was used as the binder. The reason of improving the adhesion and cohesion strength is the suitable thermal shrinkage, the uniform distribution and densification structure of α‐alumina. Furthermore, optimization of the coating formulation with α‐alumina as the binder has been performed. Finally, the catalyst prepared under the optimal conditions was tested by SCR and a maximum conversion rate of 97.4% was obtained. It was concluded that the use of the washcoating method with α‐alumina does not affect catalytic performance while it increases bonding strength between substrate and catalysts.     

Undesired components in the transformation of biomass pyrolysis oil into hydrocarbons on an HZSM‐5 zeolite catalyst

The results of the catalytic transformation on HZSM‐5 zeolite of mixtures of components of biomass pyrolysis oil in the 673–723 K temperature range are evidence of the need for previously separating certain components (aldehydes, oxyphenols and furfural) that undergo severe thermal degradation by forming carbonaceous deposits at the reactor inlet ducts and on the catalyst itself. The deactivation of the catalyst is a consequence of the deposition of two different types of coke: one of catalytic origin (similar to that generated in the transformation of methanol and bioethanol) and the other of thermal origin, which is produced by the aforementioned degradation. The remaining oxygenate components react to each other with synergistic effect, which means that their reactivity is higher than that of the pure components. The results show that the aqueous fraction of biomass pyrolysis oil may be transformed into hydrocarbons on acid catalysts similarly to the more familiar transformation of methanol and bioethanol. Copyright © 2005 Society of Chemical Industry     

Eco‐friendly,acrylic resin‐modified potassium silicate as water‐based vehicle for anticorrosive zinc‐rich primers

Potassium silicate binder of zinc‐rich coating was modified by adding water‐based acrylic resin. Several series of coatings containing 5, 10, and 15 wt % of acrylic and acrylic/styrene binders were added to potassium silicate. The coatings were applied on steel and the corrosion resistance of coatings was evaluated by conventional methods such as electrochemical impedance spectroscopy, corrosion potential, salt spray, and scanning electron microscopy. The results indicated that the modification of silicate binder with acrylic and acrylic/styrene led to shortening the curing time, improved corrosion protection, better dispersion of zinc particles, and enhanced salt spray resistance of resultant coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40370.     

Deactivation kinetics of a HZSM‐5 zeolite catalyst treated with alkali for the transformation of bio‐ethanol into hydrocarbons

The kinetics of deactivation by coke of a HZSM‐5 zeolite catalyst in the transformation of bioethanol into hydrocarbons has been studied. To attenuate deactivation, the following treatments have been carried out: (i) the zeolite has been subjected to a treatment with alkali to reduce the acid strength of the sites and (ii) it has subsequently been agglomerated into a macro and meso‐porous matrix of bentonite and alumina. The experimental study has been conducted in a fixed bed reactor under the following conditions: temperature, between 300 and 400°C; pressure, 1 atm; space‐time, up to 1.53 (g of catalyst) h (g of ethanol)^?1; particle size of the catalyst, between 0.3 and 0.6 mm; feed flowrate, 0.16 cm³ min^?1 of ethanol+water and 30 cm³ (NC) min^?1 of N₂; water content in the feed, up to 75 wt %; time on stream, up to 31 h. The expression for deactivation kinetics is dependent on the concentration of hydrocarbons and water in the reaction medium (which attenuates the deactivation) and, together with the kinetics at zero time on stream, allows the calculation of the evolution with time on stream of the yields and distribution of products (ethylene, propylene and butenes, C₁‐C₃ paraffins, and C₄‐C₁₂). By increasing the temperature in the 300–400°C range the role of ethylene on coke deposition is more significant than that of the other hydrocarbons (propylene, butenes and C₄‐C₁₂), which contribute to a greater extent to the formation of coke at 300°C. © 2011 American Institute of Chemical Engineers AIChE J, 58: 526–537, 2012.     

Oxidation resistance of SiC nanowires reinforced SiC coating prepared by a CVD process on SiC‐coated C/C composites

Oxidation protective SiC nanowires‐reinforced SiC (SiCNWs‐SiC) coating was prepared on pack cementation (PC) SiC‐coated carbon/carbon (C/C) composites by a simple chemical vapor deposition (CVD) process. This double‐layer SiCNWs‐SiC/PC SiC‐coating system on C/C composites not only has the advantages of SiC buffer layer but also has the toughening effects of SiCNWs. The microstructure and phase composition of the nanowires and the coatings were examined by SEM, TEM, and XRD. The single‐crystalline β‐SiC nanowires with twins and stacking faults were deposited uniformly and oriented randomly with diameter of 50‐200 nm and length ranging from several to tens micrometers. The dense SiCNWs‐SiC coating with some closed pores was obtained by SiC nanocrystals stacked tightly with each other on the surface of SiCNWs. After introducing SiCNWs in the coating system, the oxidation resistance is effectively improved. The oxidation test results showed that the weight loss of the SiCNWs‐SiC/PC SiC‐coated samples was 4.91% and 1.61% after oxidation at 1073 K for 8 hours and at 1473 K for 276 hours, respectively. No matter oxidation at which temperature, the SiCNWs‐SiC/PC SiC‐coating system has better anti‐oxidation property than the single‐layer PC SiC coating or the double‐layer CVD SiC/PC SiC coating without SiCNWs.     

Durable flame‐retardant and antidroplet finishing of polyester fabrics with flexible polysiloxane and phytic acid through layer‐by‐layer assembly and sol–gel process

A three‐layer functional coating was prepared through layer‐by‐layer (LbL) assembly and a sol–gel process. The multilayered coating was composed of a phytic acid (PA) coating dipped between two layers of flexible polysiloxane coatings and was deposited on the polyester fabric by LbL assembly. Flammability tests indicated that the multilayer coating prevented droplet generation during combustion. The PA also absorbed the reactive free radicals to reduce the flame‐burning rate. After being soaked for only 20 min in PA solution, the fabric exhibited self‐extinguishing properties and antidroplet effect during the vertical flame test, while cone calorimetry confirmed that the coated fabric exhibited a 65% decrease in the peak heat release rate and reduced the total amount of smoke released by 72%. After washing the coated fabric 45 times, there was no significant decrease in the phosphorus content and the limiting oxygen index of coated fabrics. Thus, the coating synthesized in this study is an effective method of constructing durable, functional coatings on the surface of fabrics. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46414.     

Screening of Fe–BEA catalysts for wet hydrogen peroxide oxidation of crude olive mill wastewater under mild conditions

A series of Fe–BEA catalysts, differing in the amount of iron have been characterized by XRD, BET surface area, UV–vis spectroscopy and chemical analysis. The zeolite samples have been tested as heterogeneous catalysts for the wet hydrogen peroxide oxidation of crude olive mill wastewaters (OMW) under very mild conditions (at 28 °C and atmospheric pressure). All experiments were performed on a laboratory scale set-up.BSE-1/3 catalyst with a moderate Fe content (Fe/Al = 1.19) showed the best results in terms of catalytic activity and loss of active species into the aqueous solutions. The stability of Fe species has been shown to be strongly dependent on the Fe environment into the zeolite framework.Over the selected catalyst, application of catalytic procedure on diluted OMW solution permitted high removal efficiencies of pollutants. The process produces a removal capacity of 28% of total organic carbon (TOC), 40% of total phenols, 30% of chemical oxygen demand (COD) and 59% of colour, just after 12 h. 5-Day biochemical oxygen demand (BOD₅), and toxicity towards the bioluminescent bacteria Vibrio fischeri were selected to follow the performance of this process in terms of reducing the ecotoxicity of OMW. Results showed an increase in the biodegradability of the treated sample and a decrease of the microtoxicity from 100% to 70% load towards V. fischeri.Occurrence of small catalyst deactivation by carbonaeous during the oxidation reaction was observed through scanning electron microscopy (SEM) and elemental analysis.     

高硅铝比小晶粒NaY分子筛/高岭土复合物的合成及其催化裂化性能

以两种不同粒径的高岭土为原料,采用水热法合成了高硅铝比小晶粒NaY分子筛/高岭土复合物,通过XRD、SEM、晶粒度分析和N₂物理吸附等表征手段对复合物进行了结构和形貌表征。结果表明,与商品NaY相比,高岭土合成样品的结构稳定性和水热稳定性显著提高,以细化高岭土为原料合成样品的晶粒尺寸达310 nm,比表面积达807 m²·g^-1。以改性NaY分子筛/高岭土复合物为活性组分制备了催化裂化催化剂,采用NH₃程序升温脱附(NH₃-TPD)技术对其酸性特征进行了分析,并在小型微反装置上对其重油催化裂化性能进行了评价。研究结果发现,随着骨架硅铝比增大,催化剂表面酸中心强度增加,而酸量下降。采用细化高岭土合成的NaY分子筛/高岭土复合物的分子筛晶粒更小,催化剂酸中心数量以及催化裂化性能均大幅度提升。随着高温焙烧高岭土/偏高岭土质量比的增加,合成产物中的高岭土基质含量增加,催化剂表面酸中心强度下降。以原料高温焙烧高岭土/偏高岭土质量比为0.5,骨架硅铝比为6.1(摩尔比)的样品制备的催化剂,去柴重油转化率高达85.4%,同时有高达64.2%的汽油收率,表现出优异的重油催化裂化性能。