Promoting active site renewal in heterogeneous olefin metathesis catalysts.

As an atom-efficient strategy for the large-scale interconversion of olefins, heterogeneously catalysed olefin metathesis sees commercial applications in the petrochemical, polymer and speciality chemical industries1. Notably, the thermoneutral and highly selective cross-metathesis of ethylene and 2-butenes1 offers an appealing route for the on-purpose production of propylene to address the C3 shortfall caused by using shale gas as a feedstock in steam crackers2,3. However, key mechanistic details have remained ambiguous for decades, hindering process development and adversely affecting economic viability4 relative to other propylene production technologies2,5. Here, from rigorous kinetic measurements and spectroscopic studies of propylene metathesis over model and industrial WOx/SiO2 catalysts, we identify a hitherto unknown dynamic site renewal and decay cycle, mediated by proton transfers involving proximal Brønsted acidic OH groups, which operates concurrently with the classical Chauvin cycle. We show how this cycle can be manipulated using small quantities of promoter olefins to drastically increase steady-state propylene metathesis rates by up to 30-fold at 250 °C with negligible promoter consumption. The increase in activity and considerable reduction of operating temperature requirements were also observed on MoOx/SiO2 catalysts, showing that this strategy is possibly applicable to other reactions and can address major roadblocks associated with industrial metathesis processes.

Synthesis and Characterization of Silicoaluminophosphate CIT-16P and Its Transformation to SAPO-17.

A silicoaluminophosphate molecular sieve, CIT-16P, is synthesized using butane-1,4-bis(quinuclidinium) [(C7H13N)-(CH2)4-(NC7H13)]2+ dihydroxide (DiQ-C4-(OH)2) as an organic structure-directing agent (OSDA). Upon the removal of the OSDA, either by thermal treatment in air at temperatures exceeding 490 °C or by extended ozone treatment at 150 °C, CIT-16P transforms to SAPO-17 (ERI topology). The structure solution of CIT-16P in its as-synthesized form is obtained using a Rietveld refinement of the powder X-ray diffraction pattern. The primary composite building units (CBUs) of CIT-16P are highly distorted cancrinite (can) CBUs that transform into stable can units of the ERI-type framework as a result of the OSDA removal. The distortion of can CBU is maintained without transformation by the presence of tightly bound DiQ-C4 dications in the as-synthesized form of CIT-16P. The transformed material is characterized and evaluated as a catalyst in the methanol-to-olefins (MTO) reaction. The catalytic behavior of the formed SAPO-17 (Si/T-atom = 0.022) (T = Si + Al + P) at 400 °C and WHSV of 1.3 h-1 produces elevated C3+ olefin products (i.e., propylene, butenes, and pentenes) in early stages of the reaction. However, as the reaction proceeds, the C3+ fraction decreases in favor of more ethylene.

Further Studies on How the Nature of Zeolite Cavities That Are Bounded by Small Pores Influences the Conversion of Methanol to Light Olefins.

A series of small-pore zeolites are synthesized and investigated as catalysts for the methanol-to-olefins (MTO) reaction. Small-pore zeolites SSZ-13, SSZ-16, SSZ-27, SSZ-28, SSZ-52, SSZ-98, SSZ-99, SSZ-104, SSZ-105 and an ITQ-3-type material are synthesized, and the results from their use as catalytic materials in the MTO reaction compared to those obtained from SAPO-34. The production of propane that tends to correlate with catalytic material lifetime (higher initial propane yields lead to shorter lifetimes) declines with increasing Si/Al (as has been observed previously for SSZ-13), and a larger cage dimension leads to higher propane yields at a fixed Si/Al. Data from these materials and others reported previously, for example, SSZ-39 and Rho, that were tested at the same reaction conditions, revealed four different patterns of light olefin selectivities: 1) ethylene greater than propylene with low butene, for example, SSZ-17, SSZ-98, SSZ-105, 2) ethylene equal to propylene and low butene, for example, SAPO-34, SSZ-13, SSZ-16, SSZ-27, SSZ-52, SSZ-99, SSZ-104, 3) propylene greater than ethylene with butene similar to ethylene, for example, SSZ-28, SSZ-39, and 4) ethylene equal to propylene equal to butene, for example, Rho. No clear relationships between zeolite cage architecture and light olefin selectivity emerged from this investigation, although several trends are presented as suggestions for further study.

CIT-9: A Fault-Free Gmelinite Zeolite.

A synthetic, fault-free gmelinite (GME) zeolite is prepared using a specific organic structure-directing agent (OSDA), cis-3,5-dimethylpiperidinium. The cis-isomers align in the main 12-membered ring (MR) channel of GME. Trans-isomer OSDA leads to the small-pore zeolite SSZ-39 with the OSDA in its cages. Data from N2 -physisorption and rotation electron diffraction provide evidence for the openness of the 12 MR channel in the GME 12×8×8 pore architecture and the absence of stacking faults, respectively. CIT-9 is hydrothermally stable when K+ -exchanged, while in the absence of exchange, the material transforms into an aluminous AFI-zeolite. The process of this phase-change was followed by in situ variable temperature powder X-ray diffraction. CIT-9 has the highest Si/Al ratio reported for GME, and along with its good porosity, opens the possibility of using GME in a variety of applications including catalysis.

Non-Electroconductive Polymer Coating on Graphite Mitigating Electrochemical Degradation of PTFE for a Dry-Processed Lithium-Ion Battery Anode.

Polytetrafluoroethylene (PTFE)-based dry process for lithium-ion batteries is gaining attention as a battery manufacturing scheme can be simplified with drastically reducing environmental damage. However, the electrochemical instability of PTFE in a reducing environment has hampered the realization of the high-performance dry-processed anode. In this study, we present a non-electroconductive and highly ionic-conductive polymer coating on graphite to mitigate the electrochemical degradation of the PTFE binder and minimize the coating resistance. Poly(ethylene oxide) (PEO) and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) coatings on the anode material effectively inhibit the electron transfer from graphite to PTFE, thereby alleviating the PTFE breakdown. The graphite polymer coatings improved initial Coulombic efficiencies of full cells from 67.2% (bare) to 79.1% (PEO) and 77.8% (P(VDF-TrFE-CFE)) and increased initial discharge capacity from 157.7 mAh g(NCM)-1 (bare) to 185.1 mAh g(NCM)-1 (PEO) and 182.5 mAh g(NCM)-1 (P(VDF-TrFE-CFE)) in the full cells. These outcomes demonstrate that PTFE degradation in the anode can be surmounted by adjusting the electron transfer to the PTFE.

Preparation and exceptional lithium anodic performance of porous carbon-coated ZnO quantum dots derived from a metal-organic framework.

Hierarchically porous carbon-coated ZnO quantum dots (QDs) (~3.5 nm) were synthesized by a one-step controlled pyrolysis of the metal-organic framework IRMOF-1. We have demonstrated a scalable and facile synthesis of carbon-coated ZnO QDs without agglomeration by structural reorganization. This unique microstructure exhibits outstanding electrochemical performance (capacity, cyclability, and rate capability) when evaluated as an anode material for lithium ion batteries.

Effect of a Multiple Reduction Die on the Residual Stress of Drawn Materials.

Residual stress may influence the mechanical behavior and durability of drawn materials. Thus, this study develops a multiple reduction die (MRD) that can reduce residual stress during the drawing process. The MRD set consists of several die tips, die cases, and lubricating equipment. All the die tips of the MRD were disposed of simultaneously. Finite element analysis of the drawing process was performed according to the reduction ratio of each die tip, and the variables in drawing process with the MRD were optimized using a deep neural network to minimize the residual stress. Experiments on the drawing process with the conventional die and MRD were performed to evaluate the residual stress and verify the effectiveness of the MRD. The results of X-ray diffraction measurements indicated that the axial and hoop residual stresses on the surface were dramatically reduced.

Genotyping of chimerical BCR-ABL1 RNA in chronic myeloid leukemia by integrated DNA chip.

Chronic myelogenous leukemia (CML) and Philadelphia chromosome-positive (Ph(+)) acute lymphoblastic leukemia (ALL) are associated with fusion of the BCR and ABL1 genes by chromosome translocation. The chimerical BCR-ABL1 gene encodes different fusion proteins that vary in size, depending on the breakpoint in the BCR region. Different types of fusion genes in CML and Ph(+) ALL are thought to be related to the clinical course and outcome of each patient. Currently, the genotypes are determined by PCR, followed by gel electrophoresis or DNA sequencing (among other methodologies). Our major aim was to develop a diagnostic method for CML genotyping by means of an integrated process of DNA microarray. Here, we describe a method of integrated multiplex reverse transcription, asymmetric PCR, and hybridization, all in the same reaction mixture in a chamber assembled on the surface of capture oligonucleotide probes immobilized on a glass slide. The integrated system successfully identified the four predominant types of chimerical BCR-ABL1 RNA (b3a2, b2a2, e1a2, and c3a2), which together account for 98% of CML cases. The integrated multiplex system also had a high sensitivity of detection (as little as 200 molecules of target RNA molecules). The integrated process saves time and effort, and it also the advantage of minimizing the steps needed for automated detection of different types of chimerical CML RNA.