The exothermic oxidative dehydrogenation of propane reaction to generate propene has the potential to be a game-changing technology in the chemical industry. However, even after decades of research, selectivity to propene remains too low to be commercially attractive because of overoxidation of propene to thermodynamically favored CO Here, we report that hexagonal boron nitride and boron nitride nanotubes exhibit unique and hitherto unanticipated catalytic properties, resulting in great selectivity to olefins. As an example, at 14% propane conversion, we obtain selectivity of 79% propene and 12% ethene, another desired alkene. Based on catalytic experiments, spectroscopic insights, and ab initio modeling, we put forward a mechanistic hypothesis in which oxygen-terminated armchair boron nitride edges are proposed to be the catalytic active sites.

Hexagonal boron nitride (h-BN) and boron nitride nanotubes (BNNT) were recently reported as highly selective catalysts for the oxidative dehydrogenation (ODH) of alkanes to olefins in the gas phase. Previous studies revealed a substantial increase in surface oxygen content after exposure to ODH conditions (heating to ca. 500 °C under a flow of alkane and oxygen); however, the complexity of these materials has thus far precluded an in-depth understanding of the oxygenated surface species. In this contribution, we combine advanced NMR spectroscopy experiments with scanning electron microscopy and soft X-ray absorption spectroscopy to characterize the molecular structure of the oxygen functionalized phase that arises on h-BN and BNNT following catalytic testing for ODH of propane. The pristine BN materials are readily oxidized and hydrolyzed under ODH reaction conditions to yield a phase consisting of three-coordinate boron sites with variable numbers of hydroxyl and bridging oxide groups which is denoted B(OH)xO3-x (where x = 0-3). Evidence for this robust oxide phase revises previous literature hypotheses of hydroxylated BN edges as the active component on h-BN.

Seven new homoleptic complexes of the form A2[M(pin(F))2] have been synthesized with the dodecafluoropinacolate (pin(F))(2-) ligand, namely (Me4N)2[Fe(pin(F))2], 1; (Me4N)2[Co(pin(F))2], 2; ((n)Bu4N)2[Co(pin(F))2], 3; {K(DME)2}2[Ni(pin(F))2], 4; (Me4N)2[Ni(pin(F))2], 5; {K(DME)2}2[Cu(pin(F))2], 7; and (Me4N)2[Cu(pin(F))2], 8. In addition, the previously reported complexes K2[Cu(pin(F))2], 6, and K2[Zn(pin(F))2], 9, are characterized in much greater detail in this work. These nine compounds have been characterized by UV-vis spectroscopy, cyclic voltammetry, elemental analysis, and for paramagnetic compounds, Evans method magnetic susceptibility. Single-crystal X-ray crystallographic data were obtained for all complexes except 5. The crystallographic data show a square-planar geometry about the metal center in all Fe (1), Ni (4), and Cu (6, 7, 8) complexes independent of countercation. The Co species exhibit square-planar (3) or distorted square-planar geometries (2), and the Zn species (9) is tetrahedral. No evidence for solvent binding to any Cu or Zn complex was observed. Solvent binding in Ni can be tuned by the countercation, whereas in Co only strongly donating Lewis solvents bind independent of the countercation. Indirect evidence (diffuse reflectance spectra and conductivity data) suggest that 5 is not a square-planar compound, unlike 4 or the literature K2[Ni(pin(F))2]. Cyclic voltammetry studies reveal reversible redox couples for Ni(III)/Ni(II) in 5 and for Cu(III)/Cu(II) in 8 but quasi-reversible couples for the Fe(III)/Fe(II) couple in 1 and the Co(III)/Co(II) couple in 2. Perfluorination of the pinacolate ligand results in an increase in the central C-C bond length due to steric clashes between CF3 groups, relative to perhydropinacolate complexes. Both types of pinacolate complexes exhibit O-C-C-O torsion angles around 40°. Together, these data demonstrate that perfluorination of the pinacolate ligand makes possible highly unusual and coordinatively unsaturated high-spin metal centers with ready thermodynamic access to rare oxidation states such as Ni(III) and Cu(III).

A set of new compounds are formed upon mixing of titanium­(IV) alkoxides with tin­(II) dicarboxylates or tin­(IV) dialkyl dicarboxylates. These mixed Ti/Sn catalysts outperform titanium alkoxides or tin complexes alone as polyesterification catalysts. However, the tin complexes employed are toxic, and efforts are underway to remove them from environmental circulation. This study elucidates the structures generated of mixed Ti/Sn complexes and how they lead to improved reactivity. A suite of characterization techniques was utilized in structural elucidation including 1H, 13C­{1H}, and 119Sn NMR, as well as 13C–1H HSQC, 1H–1H COSY, 119Sn–1H HMQC (heteronuclear multiple quantum coherence), DOSY (diffusion-ordered spectroscopy) NMR, and ASAP-MS (atmospheric solids analysis probe–mass spectrometry). These characterization techniques led to the identification of Sn–Ti heterobimetallic dimers, regardless of the tin source (viz., Sn­(II) or Sn­(IV)). The greater stability of the catalysts to agglomeration was identified ex situ by UV–vis spectroscopy by observing colloid formation. Probe reactions of Fischer esterification and transesterification were used to characterize catalyst robustness under reaction conditions and catalyst activity relative to pure Ti or Sn complexes. This set of techniques allows for characterization of nontrivial mixed esterification catalysts and will be able to be applied to nontoxic mixtures in the future as a step toward improving sustainable catalysis.

In this contribution we investigate the aerobic propylene epoxidation over a Ag/KNO 3 /CaCO 3 catalyst. The catalytic performance and surface speciation of the catalyst depends on the concentrations of feed modifiers such as ethyl chloride and nitric oxide, added to the feed to improve the selectivity by suppressing total combustion to CO 2 . After a kinetic character-ization of the system, we investigate the kinetics in the presence of CO 2 . We demonstrate that CO 2 alters the rate dependence in both reactants, affects the activation of O 2 , and results in the same maximum rate of propylene oxide formation.[a] Dr.

Raman spectroscopy is a widely employed tool for characterization of heterogeneous catalysts, although it suffers somewhat from poor sensitivity at low concentrations or under in situ conditions. In this article, we describe the use of a variation of surface-enhanced Raman spectroscopy known as shell-isolated nanoparticle-enhanced Raman spectroscopy for enhancing the sensitivity of supported metal oxide catalysts. We present a general method in which we drop-cast Au@SiO2 nanoparticles onto metal oxide-functionalized 2D films, monoliths, or pelletized powder samples to increase the Raman signal. These Au@SiO2 shell-isolated nanoparticles act as optical antennae that receive far-field radiation from the Raman laser and enhance the local electromagnetic field at the catalyst surface. We observe enhancements in Raman signals for vanadium and niobium oxide on various supports including monolithic materials, as well as the enhancement of interfacial V–O–Si vibrations on powdered silica-supported vanadium oxide catalysts that contain dispersed vanadium oxide species at ambient conditions and dehydrated up to 400 °C.

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