Characterization of LaRhO3 perovskites for dry (CO2) reforming of methane (DRM)

This work reports on the characterization of LaRhO₃ perovskite as a catalyst for dry reforming of methane. The catalyst was studied using CH₄-temperature programmed reduction (TPR), H₂-TPR, and temperature programmed surface reaction (TPSR), and the changes in the crystal structure of the catalyst due to these treatments were studied by X-ray diffraction (XRD). XRD pattern of the freshly calcined perovskites showed the formation of highly crystalline LaRhO₃ and La₂O₃ phases. H₂-TPR of the fresh calcined catalyst showed a shoulder at 342°C and a broad peak at 448°C, suggesting that the reduction of Rh in perovskite occurs in multiple steps. XRD pattern of the reduced catalyst suggests complete reduction of the LaRhO₃ phase and the formation of metallic Rh and minor amounts of La(OH)₃. The CH4-TPR data show qualitatively similar results as H₂-TPR, with a shoulder and a broad peak in the same temperature range. Following the H₂-TPR up to 950°C, the same batch of catalyst was oxidized by flowing 5 vol. % O₂/He up to 500°C and a second H₂-TPR (also up to 950°C) was conducted. This second H₂-TPR differed significantly from that of the fresh calcined catalyst. The single sharp peak at 163°C in the second H₂-TPR suggests a significant change in the catalyst, probably causedby the transformation of about 90 % of the perovskite into Rh/La₂O₃. This was confirmed by the XRD studies of the catalyst reduced after the oxidation at 500°C. TPSR of the dry reforming reaction on the fresh calcined catalyst showed CO and H₂ formation starting at 400°C, with complete consumption of the reactants at 650°C. The uneven consumption of reactants between 400°C and 650°C suggests that reactions other than DRM occur, including reverse water gas shift (RWGS) and the Boudouard reaction (BR), probably as a result of in-situ changes in the catalyst, consistent with the H₂-TPR results. TPSR, after a H₂-TPR up to 950°C, showed that the dry reforming reaction did not light off until 570°C, which is much higher temperature than the one observed using fresh calcined catalyst. This shows that the uniform sites produced during the 950°C H₂-TPR are catalytically less active than those of the fresh calcined catalyst, and that no significant side reactions such as RWGS or the Boudouard reaction occur. This suggests that reduction leads to the formation of a single type of sites which do not catalyze simultaneous side reactions.     

Combined in situ XRD and in situ XANES studies on the reduction behavior of a rhenium promoted cobalt catalyst

A 10% Co-4% Re/(2% Zr/SiO(2)) catalyst was prepared by co-impregnation using a silica support modified by 2% Zr. The catalyst was characterized by temperature programmed reduction (TPR), in situ XRD and in situ XANES analysis where it was simultaneously exposed to H(2) using a temperature programmed ramp. The results showed the two step reduction of large crystalline Co(3)O(4) with CoO as an intermediate. TPR results showed that the reduction of highly dispersed Co(3)O(4) was facilitated by reduced rhenium by a H(2)-spillover mechanism. In situ XRD results showed the presence of both, Co-hcp and Co-fcc phases in the reduced catalyst at 400 °C. However, the Co-hcp phase was more abundant, which is thought to be the more active phase as compared to the Co-fcc phase for CO hydrogenation. CO hydrogenation at 270 °C and 5 bar pressure produces no detectable change in the phases during the time of experiment. In situ XANES results showed a decrease in the metallic cobalt in the presence of H(2)/CO, which can be attributed due to oxidation of the catalyst by reaction under these conditions.     

The emission spectrum of ICl: Identification and analysis of the D′(2) → A′(2) transition

The emission spectrum of ICl is recorded and analyzed for the separated isotopomers ¹²⁷I³⁵Cl and ¹²⁷I³⁷Cl. The strongest peak near 4300 A is due mainly to D′ → A′, but with a significant contribution from β(1) → A(1). Several weaker band systems are analyzed to give information about two other bound valence states, not previously reported.     

Towards a general solid phase approach for the iterative synthesis of conjugated oligomers using a germanium based linker--first solid phase synthesis of an oligo-(triarylamine)

The development of a germanium-based linker system for the solid phase synthesis (SPS) of 3-(n-hexyl)thiophene oligomers and the first SPS of triarylamine oligomers via iterative chain extension is described. The efficiency of the key steps in the oligomer syntheses and their compatibility with the germanium linker are demonstrated by the SPS of bi-[3-(n-hexyl)thiophene] 19 and ter-(triarylamine) 50. The use of a germanium-based linker in combination with appropriately selected silicon-based blocking/protecting groups allows double coupling to drive the key cross coupling steps to completion hence minimising deletion sequences and also allows for traceless and potentially functionalisative cleavage from the resin. The latter feature has yet to be fully explored but towards this end the first ipso-borodegermylation reaction of a 2-germyl-3-(n-hexyl)thiophene is presented.     

Copper-free click--a promising tool for pre-targeted PET imaging

The copper-free click (CFC) reaction has been evaluated for its potential application to in vivo pre-targeting for PET imaging. A promising biodistribution profile is demonstrated when employing [(18)F]2-fluoroethylazide ([(18)F]1) and optimisation of the CFC reaction with a series of cyclooctynes shows that reactions proceed efficiently with tantalizing opportunities for application-specific tuning.     

Total synthesis of the Amaryllidaceae alkaloid clivonine

Two syntheses of the Amaryllidaceae alkaloid clivonine (1) are described. Both employ previously reported 7-arylhydrindane 6 as an intermediate but differ in the method employed for subsequent introduction of what becomes the ring-B lactone carbonyl carbon (C7). The synthesis featuring a Bischler-Napieralski reaction for this transformation constitutes the first asymmetric synthesis of natural (+)-clivonine. Crystal structures for compounds (±)-13, (±)-16, (-)-20 and (±)-28 are also reported.     

Kinetic Resolution of 2-Substituted Indolines by N-Sulfonylation using an Atropisomeric 4-DMAP-N-oxide Organocatalyst

The first catalytic kinetic resolution by N-sulfonylation is described. 2-Substituted indolines are resolved (s=2.6–19) using an atropisomeric 4-dimethylaminopyridine-N-oxide (4-DMAP-N-oxide) organocatalyst. Use of 2-isopropyl-4-nitrophenylsulfonyl chloride is critical to the stereodiscrimination and enables facile deprotection of the sulfonamide products with thioglycolic acid. A qualitative model that accounts for the stereodiscrimination is proposed.     

(±)-trans,cis-4-Hydroxy-5,6-di-O-isopropylidenecyclohex-2-ene-1-one: synthesis and facile dimerization to decahydrodibenzofurans

An efficient synthesis of (±)-trans,cis-4-hydroxy-5,6-di-O-isopropylidenecyclohex-2-ene-1-one (3) has been developed from acetonide-protected meso-1,2-dihydrocatechol derivative 1 via photooxygenation, then Kornblum-DeLaMare rearrangement. The product is unstable unless its 4-hydroxy group is protected, as it undergoes facile dimerization in solution to a 1:1 mixture of diastereoisomeric decahydrodibenzofurans 8 and 9. A new synthesis of the dihydrocatechol 1 from 1,3-cyclohexadiene has also been developed.     

Design and Synthesis of Copper–Cobalt Catalysts for the Selective Conversion of Synthesis Gas to Ethanol and Higher Alcohols

Combining quantum‐mechanical simulations and synthesis tools allows the design of highly efficient CuCo/MoO_x catalysts for the selective conversion of synthesis gas (CO+H₂) into ethanol and higher alcohols, which are of eminent interest for the production of platform chemicals from non‐petroleum feedstocks. Density functional theory calculations coupled to microkinetic models identify mixed Cu–Co alloy sites, at Co‐enriched surfaces, as ideal for the selective production of long‐chain alcohols. Accordingly, a versatile synthesis route is developed based on metal nanoparticle exsolution from a molybdate precursor compound whose crystalline structure isomorphically accommodates Cu²⁺ and Co²⁺ cations in a wide range of compositions. As revealed by energy‐dispersive X‐ray nanospectroscopy and temperature‐resolved X‐ray diffraction, superior mixing of Cu and Co species promotes formation of CuCo alloy nanocrystals after activation, leading to two orders of magnitude higher yield to high alcohols than a benchmark CuCoCr catalyst. Substantiating simulations, the yield to high alcohols is maximized in parallel to the CuCo alloy contribution, for Co‐rich surface compositions, for which Cu phase segregation is prevented.