The nature behind the promotional effect of phosphorus on the catalytic performance and hydrothermal stability of zeolite H‐ZSM‐5 has been studied using a combination of 27Al and 31P MAS NMR ...spectroscopy, soft X‐ray absorption tomography and n‐hexane catalytic cracking, complemented with NH3 temperature‐programmed desorption and N2 physisorption. Phosphated H‐ZSM‐5 retains more acid sites and catalytic cracking activity after steam treatment than its non‐phosphated counterpart, while the selectivity towards propylene is improved. It was established that the stabilization effect is twofold. First, the local framework silico‐aluminophosphate (SAPO) interfaces, which form after phosphatation, are not affected by steam and hold aluminum atoms fixed in the zeolite lattice, preserving the pore structure of zeolite H‐ZSM‐5. Second, the four‐coordinate framework aluminum can be forced into a reversible sixfold coordination by phosphate. These species remain stationary in the framework under hydrothermal conditions as well. Removal of physically coordinated phosphate after steam‐treatment leads to an increase in the number of strong acid sites and increased catalytic activity. We propose that the improved selectivity towards propylene during catalytic cracking can be attributed to local SAPO interfaces located at channel intersections, where they act as impediments in the formation of bulky carbenium ions and therefore suppress the bimolecular cracking mechanism.
Application of microscopy, spectroscopy and tomography techniques in the study of phosphated zeolite H‐ZSM‐5 has revealed that phosphorus‐framework aluminum interactions contribute to the hydrothermal stabilization of the zeolite lattice (see figure). Decrease in dimensions of internal framework cavities, due to the presence of phosphates, improves propylene selectivity during n‐hexane cracking.
A triethylaluminium(TEAl)‐modified Phillips ethylene polymerisation Cr/Ti/SiO2 catalyst has been developed with two distinct active regions positioned respectively in the inner core and outer shell ...of the catalyst particle. DRIFTS, EPR, UV‐Vis‐NIR DRS, STXM, SEM‐EDX and GPC‐IR studies revealed that the catalyst produces simultaneously two different polymers, i.e., low molecular weight linear‐chain polyethylene in the Ti‐abundant catalyst particle shell and high molecular weight short‐chain branched polyethylene in the Ti‐scarce catalyst particle core. Co‐monomers for the short‐chain branched polymer were generated in situ within the TEAl‐impregnated confined space of the Ti‐scarce catalyst particle core in close proximity to the active sites that produced the high molecular weight polymer. These results demonstrate that the catalyst particle architecture directly affects polymer composition, offering the perspective of making high‐performance polyethylene from a single reactor system using this modified Phillips catalyst.
Two‐in‐one: A novel triethylaluminium‐modified Phillips Cr/Ti/SiO2 ethylene polymerisation catalyst with two distinct active regions has been developed. STXM was used as a micro‐spectroscopy method to discriminate between the active sites producing low molecular weight linear chain and high molecular weight short‐chain branched polyethylene within a single catalyst particle.
Phosphorus and microporous aluminosilicates, better known as zeolites, have a unique but poorly understood relationship. For example, phosphatation of the industrially important zeolite H-ZSM-5 is a ...well-known, relatively inexpensive and seemingly straightforward post-synthetic modification applied by the chemical industry not only to alter its hydrothermal stability and acidity, but also to increase its selectivity towards light olefins in hydrocarbon catalysis. On the other hand, phosphorus poisoning of zeolite-based catalysts, which are used for removing nitrogen oxides from exhaust fuels, poses a problem for their use in diesel engine catalysts. Despite the wide impact of phosphorus-zeolite chemistry, the exact physicochemical processes that take place require a more profound understanding. This review article provides the reader with a comprehensive and state-of-the-art overview of the academic literature, from the first reports in the late 1970s until the most recent studies. In the first part an in-depth analysis is undertaken, which will reveal universal physicochemical and structural effects of phosphorus-zeolite chemistry on the framework structure, accessibility, and strength of acid sites. The second part discusses the hydrothermal stability of zeolites and clarifies the promotional role that phosphorus plays. The third part of the review paper links the structural and physicochemical effects of phosphorus on zeolite materials with their catalytic performance in a variety of catalytic processes, including alkylation of aromatics, catalytic cracking, methanol-to-hydrocarbon processing, dehydration of bioalcohol, and ammonia selective catalytic reduction (SCR) of NOx. Based on these insights, we discuss potential applications and important directions for further research.
The formation of hydrocarbon pool (HCP) species during methanol‐to‐olefin (MTO) and ethanol‐to‐olefin (ETO) processes have been studied on individual micron‐sized SAPO‐34 crystals with a combination ...of in situ UV/Vis, confocal fluorescence, and synchrotron‐based IR microspectroscopic techniques. With in situ UV/Vis microspectroscopy, the intensity changes of the λ=400 nm absorption band, ascribed to polyalkylated benzene (PAB) carbocations, have been monitored and fitted with a first‐order kinetics at low reaction temperatures. The calculated activation energy (Ea) for MTO, approximately 98 kJ mol−1, shows a strong correlation with the theoretical values for the methylation of aromatics. This provides evidence that methylation reactions are the rate‐determining steps for the formation of PAB. In contrast for ETO, the Ea value is approximately 60 kJ mol−1, which is comparable to the Ea values for the condensation of light olefins into aromatics. Confocal fluorescence microscopy demonstrates that during MTO the formation of the initial HCP species are concentrated in the outer rim of the SAPO‐34 crystal when the reaction temperature is at 600 K or lower, whereas larger HCP species are gradually formed inwards the crystal at higher temperatures. In the case of ETO, the observed egg‐white distribution of HCP at 509 K suggests that the ETO process is kinetically controlled, whereas the square‐shaped HCP distribution at 650 K is indicative of a diffusion‐controlled process. Finally, synchrotron‐based IR microspectroscopy revealed a higher degree of alkylation for aromatics for MTO as compared to ETO, whereas high reaction temperatures favor dealkylation processes for both the MTO and ETO processes.
Spectroscopy and kinetics hand in hand: UV/Vis microspectroscopy was used to investigate the kinetics taking place inside individual SAPO‐34 crystals during alcohol‐to‐olefin reactions. At low temperatures, formation of hydrocarbon pool (HCP) species is the primary reaction, whereas dealkylation and cracking of these species is dominant at high temperatures. Activation energies deduced from low‐temperature regions suggest distinct reaction pathways for using different alcohols (see figure; • (red)=methanol, ▪=ethanol).
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► Infrared micro-spectroscopy enables the study of individual cracking catalyst particles. ► Structural changes in the zeolite and clay component are observed upon deactivation. ► ...Industrial deactivation protocols lead to a decrease in Brønsted and Lewis acidity. ► Equilibrium catalysts display large heterogeneities in acidity.
A synchrotron-based infrared micro-spectroscopy study has been conducted to investigate the structure as well as the Brønsted and Lewis acidity of Fluid Catalytic Cracking (FCC) catalyst particles at the individual particle level. Both fresh and laboratory-deactivated catalyst particles have been studied. The applied deactivation protocols were steaming (ST), two-step cyclic deactivation (CD) and Mitchell impregnation-steam deactivation (MI). In addition, an equilibrium catalyst (Ecat) taken from a real cracking unit has been investigated. From the infrared spectra of the fresh and laboratory-deactivated samples it was clear that the zeolite component experiences partial collapse upon deactivation. Furthermore, it was found that characteristic bands, caused by the presence of clay material, are lost upon deactivation. After pyridine adsorption, the acidity of the samples could be monitored. Both Brønsted and Lewis acidity decreased in the following order: Fresh>ST>CD>MI. The Ecat sample was found to display acidity in between those of CD and MI samples. These findings are in line with earlier bulk transmission infrared as well as ammonia temperature programmed desorption measurements, which confirms the validity of acidity measurements at the single particle level. However, additional information about the distribution of Brønsted and Lewis acidity within individual catalyst particles becomes available. The developed approach reveals a larger variety in the amount of Brønsted acid sites for individual Ecat particles as compared to CD and MI particles. This observation can be attributed to the wide age distribution within industrial equilibrium catalysts and directly shows the added value of micro-spectroscopy approaches in the investigation of interparticle heterogeneities.
IntroductionA major knowledge gap in the treatment of complicated Staphylococcus aureus bacteraemia (SAB) is the optimal duration of antibiotic therapy. Safe shortening of antibiotic therapy has the ...potential to reduce adverse drug events, length of hospital stay and costs. The objective of the SAFE trial is to evaluate whether 4 weeks of antibiotic therapy is non-inferior to 6 weeks in patients with complicated SAB.Methods and analysisThe SAFE-trial is a multicentre, non-inferiority, open-label, parallel group, randomised controlled trial evaluating 4 versus 6 weeks of antibiotic therapy for complicated SAB. The study is performed in 15 university hospitals and general hospitals in the Netherlands. Eligible patients are adults with methicillin-susceptible SAB with evidence of deep-seated or metastatic infection and/or predictors of complicated SAB. Only patients with a satisfactory clinical response to initial antibiotic treatment are included. Patients with infected prosthetic material or an undrained abscess of 5 cm or more at day 14 of adequate antibiotic treatment are excluded. Primary outcome is success of therapy after 180 days, a combined endpoint of survival without evidence of microbiologically confirmed disease relapse. Assuming a primary endpoint occurrence of 90% in the 6 weeks group, a non-inferiority margin of 7.5% is used. Enrolment of 396 patients in total is required to demonstrate non-inferiority of shorter antibiotic therapy with a power of 80%. Currently, 152 patients are enrolled in the study.Ethics and disseminationThis is the first randomised controlled trial evaluating duration of antibiotic therapy for complicated SAB. Non-inferiority of 4 weeks of treatment would allow shortening of treatment duration in selected patients with complicated SAB. This study is approved by the Medical Ethics Committee VUmc (Amsterdam, the Netherlands) and registered under NL8347 (the Netherlands Trial Register). Results of the study will be published in a peer-reviewed journal.Trial registration numberNL8347 (the Netherlands Trial Register).
Starless molecular sieves: The starlike appearence of confocal fluorescence microscopy (CFM) images of large crystals of the AlPO‐5 family of microporous materials is due to the presence of barriers ...to molecular diffusion in the internal crystal architecture (see picture) rather than a star‐shaped subcrystal according to studies by CFM, focused ion beam milling, electron backscatter diffraction, and atomic force microscopy.
In this work, three industrially relevant zeolites with framework topologies of MOR, FAU and FER have been explored on their ability to form an AlPO4 phase by reaction of a phosphate precursor with ...expelled framework aluminum. A detailed study was performed on zeolite H-mordenite, using in situ STXM and soft X-ray absorption tomography, complemented with 27Al and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, XRD, FT-IR spectroscopy, and N2 physisorption. Extraframework aluminum was extracted from steam-dealuminated H-mordenite and shown to dominantly consist of amorphous AlO(OH). It was found that phosphoric acid readily reacts with the AlO(OH) phase in dealuminated H-mordenite and forms an extraframework amorphous AlPO4 phase. It was found that while AlPO4 crystallizes outside of the zeolitic channel system forming AlPO4 islands, AlPO4 that remains inside tends to stay more amorphous. In the case of ultrastable zeolite Y the FAU framework collapsed during phosphatation, due to extraction of framework aluminum from the lattice. However, using milder phosphatation conditions an extraframework AlPO4 α-cristobalite/tridymite phase could also be produced within the FAU framework. Finally, in steamed zeolite ferrierite with FER topology the extraframework aluminum species were trapped and therefore not accessible for phosphoric acid; hence, no AlPO4 phase could be formed within the structure. Therefore, the parameters to be taken into account in AlPO4 synthesis are the framework Si/Al ratio, stability of framework aluminum, pore dimensionality and accessibility of extraframework aluminum species.
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