Effect of zeolite structure on light aromatics formation during upgrading of cellulose fast pyrolysis vapor

Promising technology for the conversion of cellulose to aromatics by catalytic fast pyrolysis (CFP) was investigated using five zeolite catalysts, i.e., 5A, SAPO-34, HY, BETA and HZSM-5. The relationship between the porosity and acidity of different zeolites with product selectivity was studied. The results showed that both the acidity and pore size of the zeolite significantly affected the production of aromatics and coke, especially the bio-oil composition. The bio-oils obtained over 5A or SAPO-34 (small pore<5.5 nm) have relatively high oxygen content. The BTEXN (benzene, toluene, ethylbenzene, xylenes and naphthalene) carbon yields over weak acidic zeolites of HY and BETA are only 6.5% and 9.0%, respectively. Due to the appropriate pore size distribution and acid position, HZSM-5 gave the highest BTEXN carbon yield of 21.1%. Moreover, the coke deposited on the spent zeolites was analyzed by temperature programmed oxidation. Furthermore, three possible mechanisms that the acid sites catalyze vapor towards non-condensable gases, aromatics and coke were also studied. HZSM-5 achieved satisfactory deoxygenation and aromatic production simultaneously, made it a potential catalyst for producing light aromatics from reforming the biomass pyrolytic vapors.     

Molecular sieve as an effective barrier for methanol crossover in direct methanol fuel cells

Methanol crossover is still a significant barrier to the commercialization of direct methanol fuel cells with wide-used Nafion® membrane. Herein, molecular sieve is introduced into the design of polymer electrolyte membrane to alleviate methanol crossover. The UZM-9 zeolite with an intermediate window size of 0.42 nm can effectively separate hydrated methanol (ca. 1.10 nm) and hydrated proton (ca. 0.23 nm). The methanol diffusion rate through the membrane is effectively suppressed after modified with UZM-9, which is about four times lower than the origin Nafion® membrane. The resulted peak power density reached 80 mW cm⁻² with 2 mol L⁻¹ methanol solution feed, which is 2.5-fold higher than that of direct methanol fuel cell with commercial Nafion® membrane. These results open a promising route to alleviate methanol crossover in direct methanol fuel cells.     

Hydrocracking and hydrodesulfurization of diesel over zeolite beta-containing NiMo supported on activated red mud

NiMo nanocatalysts supported on activated red mud with different zeolite beta contents were successfully prepared by impregnation technique. Their hydrocracking and hydrodesulfurization activities were evaluated with two different kinds of diesel feed (iso diesel and heavy diesel) in a fixed bed reactor at ambient pressure and 500 °C. Physico-chemical properties of synthesized samples were characterized using the methods of XRF, XRD, FESEM, BET, FTIR and NH₃-TPD. The results indicated that zeolite incorporation resulted in a significant increase in specific surface area (BET result) and acidic strength (TPD result) of nanocatalysts. FESEM analysis confirmed that the particles size of zeolite-containing NiMo/ARM was less than 100 nm and the average size of particles was about 30 nm. Hydrocracking results illustrated that incorporation of zeolite beta improved cracking activity considerably. In addition, NiMo nanocatalyst containing 37.5 wt% of zeolite had the highest yields of desirable products (naphtha, kerosene and diesel) and the highest conversion. Moreover, the flash point and viscosity of the liquid product decreased notably the nanocatalysts with 37.5 wt% and 12.5 wt% of zeolite were able to remove approximately 96% and 72% of the sulfur content of iso diesel and heavy diesel, respectively.     

Aromatic Compounds from Lignin Liquefaction over ZSM‐5 Catalysts in Supercritical Ethanol

A systematic research about the liquefaction of alkali lignin in supercritical ethanol using ZSM‐5 zeolite catalysts is reported, which includes the synergistic effect of temperature, catalytic content, and reaction time on product yield and distribution. Fourier transform infrared and gas chromatography‐mass spectrometry analysis were carried out to evaluate the compositions of bio‐oil and solid residue. Under moderate condition, maximum conversion and yield of bio‐oil were satisfactorily high. With the help of ZSM‐5 catalyst, lignin could be successfully converted into aromatic compounds.     

ZIF-8 derived bimetallic Fe–Ni-Nanoporous carbon for enhanced oxygen reduction reaction

The development of highly efficient nοn-nοble meta? catalysts for (ОRR) in PEMFCs is at the heart of the research, yet their performance is not satisfactory. The Fe–N active sites enclosed in carbon matrix are generally agreed to be the most promising active sites for ORR. In view of this, further effort is made to increase the Fe–N active sites. Here we present the fabrication of novel FeNi bimetallic electrоcatalyst obtained from ZIF, which consists of FeNi nanоallоys incorporated in N-doped carbon (FeNi-NC) featuring carbon nanotubes and porous carbon demonstrates outstanding results for ОRR. The Fe–N and Ni–N active sites synergistically enhance the ORR activity of FeNi-NC catalyst. The FeNi-NC showed remarkable performance in KОH with the half-wave and onset potential of 0.89 V and 0.99 V vs RHE, respectively. This catalyst shows exceptional stability in methanol equivalent to Pt/C commercial. The FeNi-NC retained 71%, while Pt/C commercial retained only 59% of its original current density. The exceptional stability and activity might be associated with the interplay among FeNi active sites and N-doped carbon, the distinct nanо-structure made up of porous carbon and carbon nanotubes with a high graphitization degree.     

One pot fusion route for the synthesis of zeolite 4A using kaolin

A new process route for obtaining zeolite 4A from kaolin was realized by subjecting all raw materials needed for hydrothermal synthesis to thermal activation in one pot method. For that purpose, different routes of activation steps for kaolin, which are metakaolinization, alkali fusion and one pot fusion were investigated for a wide range of kaolin sources in order to obtain zeolite 4A product with highest crystallinity. The influence of Si/Al ratio in addition to the chemical composition of raw kaolin, i.e. quartz and iron impurity content, on the product 4A was investigated following all three activation routes. It was found that alkali fusion process allows incorporation of quartz as silicon source during the hydrothermal synthesis of zeolite 4A, which may result in a variety of products such as zeolite P and zeolite 13X. In this study, a novel approach was developed by thermal activation of a mixture of kaolin, alkali and alumina sources at once in one pot route, which was followed by hydrothermal synthesis. The current study indicates the possibility of adjusting Si/Al ratio adding Al(OH)₃ during the activation step in one pot fusion process, which resulted in synthetic zeolite 4A of higher than 90% crystallinity using low quality kaolin.     

Search for solid acid catalysts aiming at the development of bifunctional tandem catalysts for the one-pass synthesis of lower olefins via CO2 hydrogenation

The development of methodologies for CO₂ utilization is in high demand worldwide. Here, we propose bifunctional tandem catalysts of ZnZrO_x (for CO₂-to-methanol hydrogenation) and a series of solid acid catalysts (for subsequent methanol conversion to light olefins). As solid acid catalysts, we used zeolites and silicoaluminophosphates with different topologies, MOR, FER, MFI, 1BEA, CHA, and ERI, confirmed by X-ray diffraction, electron microscopy, and nitrogen adsorption-desorption. They also showed the corresponding acid properties examined by ammonia adsorption. The tandem catalysts realized a one-pass synthesis of lower olefins, while no hydrocarbons were obtained using ZnZrO_x only. According to the reaction test and ammonia adsorption, there seems to be no correlation between product yields and acid strength. The pore sizes and channel dimensionality of zeolites influence the selectivity of products; zeolites with small pores, such as MOR, SAPO-34 and ERI, are promising, while zeolites with larger pores, such as MFI, produce heavier hydrocarbons. The results provide new insight into the design of innovative catalysts for CO₂ utilization.     

Polydopamine modified Au/FAU catalytic membrane for CO preferential oxidation

A hollow-fiber-supported stable Au/FAU catalytic membrane was successfully synthesized through a polydopamine coating modification-removal strategy and used as a flow-through catalytic membrane reactor for preferential oxidation of CO. Small Au nanoparticles can be efficiently isolated by dopamine and the dopamine-derived carbon shells. The interactions between Au nanoparticles and zeolite layer support are enhanced during annealing at high temperature under an inert atmosphere. A zeolite membrane supported Au nanoparticle catalyst was obtained after the removal of carbon shells, which showed high catalytic activity and stability for the removal of CO from hydrogen.     

Enhanced hydrogen-assisted cracking of 1,3,5-triisopropylbenzene over fibrous silica ZSM-5: Influence of co-surfactant during synthesis

In this study, unique fibrous silica ZSM-5 was successfully synthesized by using three type of alcohol possessing different alkyl-chain length as the co-surfactant. The effect of diverse co-surfactant was observed in the changes of physical properties, such as crystallinity, inter-dendrimer distances and pore properties. According to the IR and temperature programmed desorption of ammonia (NH₃-TPD) analyses, all catalysts exhibited different acid strengths which could be triggered by the different amount of additional silica species. All catalysts exhibited high catalytic performance in the hydrocracking of 1,3,5-triisopropylbenzene due to the absence of diffusion limitation. However, FZSM5C3 exhibited the highest catalytic activity which corresponded to its high number of Brønsted acid sites. It was observed that different length of co-surfactant alkyl-chain has resulted in different degree of oil penetration into the microemulsion system which subsequently triggered in various inter-dendrimer distances and amount of incorporated silica species. Hence, the altered physicochemical properties led to the difference in catalytic performance due to the presence of different number of Brønsted acid sites.     

8—羟基喹啉在沸石表面行为研究中的探针作用

尝试利用８－羟基喹啉作探针,用荧光光谱技术来获得沸石外表面的新信息。研究了ＮａＹ及Ｂａ２＋、Ｃａ２＋、Ｍｇ２＋、Ａｌ３＋交换ＮａＹ沸石表面的８－羟基喹啉络合物荧光光谱。其中Ｍｇ２＋交换沸石表面形成的络合物荧光强度最强。对Ｍｇ２＋、Ｃａ２＋和Ｂａ２＋离子所形成的络合物荧光强度随金属离子半径增大而减弱,峰位规律性地向长波移动。Ｍｇ２＋交换的ＮａＹ沸石形成络合物的适宜ｐＨ值在１０～１１,Ａｌ３＋交换ＮａＹ沸石的ｐＨ值在８～１０。随吸附液ｐＨ值增加,Ｍｇ２＋和Ａｌ３＋的络合物荧光强度先增加后下降,并且峰位向短波移动。