Explore the vast range of titles available.

In general, homogeneous catalysis signifies reactions with soluble catalysts that are of the same phase as of the reactants in order to decrease the activation energy and increase the reaction rate. The aromatic halogenation substitution reaction of p-xylene to the multi-halogenated derivatives is a well-known reaction that has been studied over years. However, the recent advances in porous materials (e.g., MOFs) have re-focused the spot again on such a reaction so as to functionalize those materials. This study is concerned with the homogeneous catalytic bromination of p-xylene to 2,5-dibromo-p-xylene along with its separation and purification. Using Ferric chloride hexahydrate as catalyst, the effect of variating the bromine amount, the reaction temperature, and the reaction time have been selectively studied. The products were characterized using XRD, FTIR, and H 1 NMR Spectrometer. The best yield of 2,5-dibromo-p-xylene is at bromine/p-xylene ratio of 2:1.

Transformation of greenhouse gas CO 2 and renewable H 2 into fuels and commodity chemicals is recognized as a promising route to store fluctuating renewable energy. Although several C 1 chemicals, olefins, and gasoline have been successfully synthesized by CO 2 hydrogenation, selective conversion of CO 2 and H 2 into aromatics is still challenging due to the high unsaturation degree and complex structures of aromatics. Here we report a composite catalyst of ZnAlO x and H-ZSM-5 which yields high aromatics selectivity (73.9%) with extremely low CH 4 selectivity (0.4%) among the carbon products without CO. Methanol and dimethyl ether, which are synthesized by hydrogenation of formate species formed on ZnAlO x surface, are transmitted to H-ZSM-5 and subsequently converted into olefins and finally aromatics. Furthermore, 58.1% p -xylene in xylenes is achieved over the composite catalyst containing Si-H-ZSM-5. ZnAlO x &H-ZSM-5 suggests a promising application in manufacturing aromatics from CO 2 and H 2 . Selective conversion of CO 2 and H 2 into aromatics remains challenging due to the high unsaturation degree and complex structure of aromatics. Here the authors report a composite catalyst of ZnAlO x and H-ZSM-5 which promotes the formation of aromatics with high selectivity while inhibiting CO and CH 4 formation in CO 2 hydrogenation reactions.

With the aim to solve the serious problem of white plastic pollution, we report herein a low-cost process to quantitatively convert polyethylene terephthalate (PET) into p -xylene (PX) and ethylene glycol (EG) over modified Cu/SiO 2 catalyst using methanol as both solvent and hydrogen donor. Kinetic and in-situ Fourier-transform infrared spectroscopy (FTIR) studies demonstrate that the degradation of PET into PX involves tandem PET methanolysis and dimethyl terephthalate (DMT) selective hydro-deoxygenation (HDO) steps with the in-situ produced H 2 from methanol decomposition at 210 °C. The overall high activities are attributed to the high Cu + /Cu 0 ratio derived from the dense and granular copper silicate precursor, as formed by the induction of proper NaCl addition during the hydrothermal synthesis. This hydrogen-free one-pot approach allows to directly produce gasoline fuels and antifreeze components from waste poly-ester plastic, providing a feasible solution to the plastic problem in islands. To solve the serious problem of white plastic pollution many degradation routes are being investigated. Here the authors show a H 2 -free low-cost Cu/SiO 2 catalyzed process to quantitatively convert polyethylene terephthalate into p-xylene and ethylene glycol in one pot with methanol as both the solvent and hydrogen source at 210 °C.

The shape-selective catalysis enabled by zeolite micropore’s molecular-sized sieving is an efficient way to reduce the cost of chemical separation in the chemical industry. Although well studied since its discovery, HZSM-5′s shape-selective capability has never been fully exploited due to the co-existence of its different-sized straight channels and sinusoidal channels, which makes the shape-selective p -xylene production from toluene alkylation with the least m -xylene and o -xylene continue to be one of the few industrial challenges in the chemical industry. Rather than modifications which promote zeolite shape-selectivity at the cost of stability and reactivity loss, here inverse Al zoned HZSM-5 with sinusoidal channels predominantly opened to their external surfaces is constructed to maximize the shape-selectivity of HZSM-5 sinusoidal channels and reach > 99 % p -xylene selectivity, while keeping a very high activity and good stability ( > 220 h) in toluene methylation reactions. The strategy shows good prospects for shape-selective control of molecules with tiny differences in size. Full utilization of ZSM-5 shape-selectivity is restricted by crystal external surface acid sites and co-existence of two different sized channels. Here, the authors synthesize reverse Al zoned ZSM-5 with sinusoidal channel preferentially opened to its inert external surface to achieve 99.3% p -xylene selectivity.

P-xylene is a type of aromatic hydrocarbon that has growing biomedical and environmental importance. It has been identified as a putative biomarker for prostate cancer and its fast and selective detection in biological fluids (especially urine and blood) is critical in the diagnosis and monitoring of the disease. Similarly, removal of p-xylene from industrial effluents and wastewater is an important environmental consideration due to its toxicity and persistence. These reasons emphasize the importance of developing and calculating the performance of efficient adsorbent and electrochemical sensors for p-xylene. Here, the adsorption and sensing performance of three fullerene-based nanostructures (C 60 , BC 59 , NC 59 ) were computationally studied for p-xylene using electronic structure calculations, charge transport analysis, dipole moment calculations, and non-covalent interaction (NCI/RDG) maps. There were significant changes in electrical conductivity induced by adsorption and transduction was strongly analyte-dependent: C 60 from 1.92 × 10 − 5 to 2.93 × 10 − 4 S/m (C 60 @ p-xylene), BC 59 from 1.18 × 10 − 2 to 1.81 × 10 − 1 S/m (BC 59 @ p-xylene), NC 59 from 3.68 × 10 − 3 to 2.07 × 10 − 3 S/m (NC 59 @ p-xylene). Recovery times were ultrafast for all three complexes with the fastest recovery time being for NC 59 @ p-xylene (3.5 × 10 − 7 s), C 60  = 9.8 × 10 − 7 , and BC 59 @ p-xylene (1.9 × 10 − 5 s). Dipole-moment analysis showed significant polarization upon adsorption for the doped systems. The dipole moment increased from 1.50 to 3.91 D in BC 59 and from 1.39 to 3.05 D in NC 59 . NCI and RDG analyses found that C 60 @p-xylene is mainly affected by weak van der Waals forces. BC 59 @p-xylene shows stronger π-π interactions. NC 59 @p-xylene has intermediate but improved attractive interactions because of nitrogen doping. These trends are consistent with the adsorption energy ranking BC 59  > C 60  > NC 59 and highlight the changes in sensor response and recovery behavior. This study shows that BC 59 has the strongest adsorption and is suitable for environmental adsorption and removal of p-xylene. NC 59 , on the other hand, has extremely high conductivity modulation and ultrafast recovery, along with reasonable adsorption. This makes NC 59 the most promising candidate for detecting p-xylene in early prostate cancer detection.

The separation of xylene isomers ( para -, meta -, orth -) remains a great challenge in the petrochemical industry due to their similar molecular structure and physical properties. Porous materials with sensitive nanospace and selective binding sites for discriminating the subtle structural difference of isomers are urgently needed. Here, we demonstrate the adaptively molecular discrimination of xylene isomers by employing a NbOF 5 2− -pillared metal–organic framework (NbOFFIVE-bpy-Ni, also referred to as ZU-61) with rotational anionic sites. Single crystal X-ray diffraction studies indicate that ZU-61 with guest-responsive nanospace/sites can adapt the shape of specific isomers through geometric deformation and/or the rotation of fluorine atoms in anionic sites, thereby enabling ZU-61 to effectively differentiate xylene isomers through multiple C–H···F interactions. ZU-61 exhibited both high meta -xylene uptake capacity (3.4 mmol g −1 ) and meta -xylene/ para -xylene separation selectivity (2.9, obtained from breakthrough curves), as well as a favorable separation sequence as confirmed by breakthrough experiments: para -xylene elute first with high-purity (≥99.9%), then meta -xylene, and orth -xylene. Such a remarkable performance of ZU-61 can be attributed to the type anionic binding sites together with its guest-response properties. The separation of xylene isomers remains a great challenge in industry due to their similar molecular structure and physical properties. Here the authors demonstrate adaptively molecular discrimination of xylene isomers by employing a NbOF 5 2− -pillared metal–organic framework with rotational anionic sites.

Gas stations distributed around densely populated areas are responsible for toxic pollutant emissions such as volatile organic compounds (VOCs). This study aims to measure VOCs emission from three different kinds of gas stations to determine the extent of pollution from the gas stations and the most frequent type of VOC compound emitted. The concentrations of ambient VOCs at three refueling stations with a different type of fuels in Mashhad were monitored. The result of this study showed that CNG fuel stations are less polluting than petrol stations. In all the studied sites, the highest concentrations were related to xylene isomers, irrespective of the fuel type. Total VOCs at the supply of both compressed natural gas (CNG) and gasoline stations was 482.36 ± 563.45 µg m −3 . At a CNG station and a gasoline station, total VOC concentrations were 1363.4 ± 1975 µg m −3 and 410.29 ± 483.37 µg m −3 , respectively. The differences in concentrations of toluene and m,p-xylene between the fuel stations can be related to the quality and type of fuel, vapor recovery technology, fuel reserves, dripless nozzles, traffic density in these stations, meteorological conditions and the location of sampling sites. The combination of a sine function and a quadratic function could model the fluctuation behavior of air pollutants like m,p-xylene. In all the sites, the highest concentrations were related to xylene isomers, irrespective of the type of fuel. The changing rate of m,p-xylene pollutant in each station was also modeled in this study.

To better understand the characterization and secondary organic aerosol (SOA) formation of volatile organic compounds (VOCs) during non-haze and haze days, ambient VOCs were continuously measured by a vehicle-mounted online thermal desorption system coupled with a gas chromatography–mass spectrometry (TD–GC/MS) system in Shanghai, China. The average concentrations of VOCs in haze episodes (193.2 μg m −3 ) were almost 50% higher than in non-haze periods (130.8 μg m −3 ). VOC concentrations exhibited a bi-modal pattern in the morning and evening rush hour periods on both non-haze and haze days. The ratios of toluene to benzene (T/B) and m,p-xylene to ethylbenzene (X/E) indicated that VOCs were aged air mass transported from nearby areas. The estimated SOA yields were 12.6 ± 5.3 and 16.7 ± 6.7 μg m −3 for non-haze and haze days, respectively, accounting for 9.6 and 8.7% of the corresponding PM 2.5 concentrations, which were slightly underestimated. VOCs–sensitivity (VOCs–S) based on a PM 2.5 -dependent model was used to investigate the variation between VOCs and PM 2.5 concentrations in the morning rush hour. It was found that VOCs were more sensitive to PM 2.5 on clean days than during periods of heavy particulate pollution. VOCs–sensitivity was significantly correlated with the ratio of specific PM 2.5 to background PM 2.5 , with a simulated equation of y  = 0.84x −0.62 ( r 2  = 0.93, p  < 0.001). Our findings suggest that strategies to mitigate VOC emissions and further alleviate haze episodes in Shanghai based on reducing gasoline vehicle-related sources would be very efficient.

Single-molecule imaging is challenging but highly beneficial for investigating intermolecular interactions at the molecular level 1 – 6 . Van der Waals interactions at the sub-nanometre scale strongly influence various molecular behaviours under confinement conditions 7 – 11 . Inspired by the traditional compass 12 , here we use a para -xylene molecule as a rotating pointer to detect the host–guest van der Waals interactions in the straight channel of the MFI-type zeolite framework. We use integrated differential phase contrast scanning transmission electron microscopy 13 – 15 to achieve real-space imaging of a single para -xylene molecule in each channel. A good correlation between the orientation of the single-molecule pointer and the atomic structure of the channel is established by combining the results of calculations and imaging studies. The orientations of para -xylene help us to identify changes in the van der Waals interactions, which are related to the channel geometry in both spatial and temporal dimensions. This work not only provides a visible and sensitive means to investigate host–guest van der Waals interactions in porous materials at the molecular level, but also encourages the further study of other single-molecule behaviours using electron microscopy techniques. The orientation of a rotating para -xylene molecule in the nanochannel of a zeolite framework can be visualised by electron microscopy to determine the host–guest van der Waals interaction inside the channel.

HZSM-5@silicalite-1 catalysts were prepared by the hydrothermal method, and the structure, morphology, acidity and pore texture of core–shell catalysts were studied by XRD, SEM, TEM, NH 3 -TPD, Py-IR and N 2 adsorption/desorption isotherms in detail. Their catalytic performances were tested in the alkylation reaction of toluene with methanol. The results showed that a coating layer was formed in the form of silicalite-1 on HZSM-5. NH 3 -TPD measurements indicated that HZSM-5@silicalite-1 contained less strong acid sites but more weak acid sites than the parent HZSM-5. The selectivity of p -xylene for toluene alkylation was approximately linear with the percentage of weak acid in total acid. Under the optimal reaction conditions, the conversion of toluene was 34.15%, and the selectivity of p -xylene was 96.77%. Graphic Abstract