Interaction of lithium hydride and ammonia borane in THF

10.1039/b812576gChemical Communications435595-5597CHCO

Is It Homogeneous or Heterogeneous Catalysis Derived from [RhCp*Cl-2](2)? In Operando XAFS, Kinetic, and Crucial Kinetic Poisoning Evidence for Subnanometer Rh-4 Cluster-Based Benzene Hydrogenation Catalysis

Determining the true, kinetically dominant catalytically active species, in the classic benzene hydrogenation system pioneered by Maitlis and co-workers 34 years ago starting with [RhCp*Cl-2](2) (CP* = [eta(5)-C-5(CH3)(5)]), has proven to be one of the most challenging case studies in the quest to distinguish single-metal-based "homogeneous" from polymetallic, "heterogeneous" catalysis. The reason, this study will show, is the previous failure to use the proper combination of: (i) in operando spectroscopy to determine the dominant form(s) of the precatalyst's mass under catalysis (i.e., operating) conditions, and then crucially also (ii) the previous lack of the necessary kinetic studies, catalysis being a "wholly kinetic phenomenon" as J. Halpern long ago noted. An important contribution from this study will be to reveal the power of quantitiative kinetic poisoning experiments for distinguishing single-metal, or in the present case subnanometer Rh-4 cluster-based catalysis, from larger, polymetallic Rh(0)(n) nanoparticle catalysis, at least under favorable conditions. The combined in operando X-ray absorption fine structure (XAFS) spectroscopy and kinetic evidence provide a compelling case for Rh-4-based, with average stoichiometry "Rh4Cp*2.4Cl4Hc", benzene hydrogenation catalysis in 2-propanol with added Et3N and at 100 degrees C and 50 atm initial H-2 pressure. The results also reveal, however, that if even ca. 1.4% of the total soluble Rh(0)(n) had formed nanoparticles, then those Rh(0)(n) nanoparticles would have been able to account for all the observed benzene hydrogenation catalytic rate (using commercial, ca. 2 nm, polyethyleneglycol-dodecylether hydrosol stabilized Rh(0)(n) nanoparticles as a model system). The results-especially the poisoning methodology developed and employed-are of significant, broader interest since determining the nature of the true catalyst continues to be a central, often vexing issue in any and all catalytic reactions. The results are also of fundamental interest in that they add to a growing body of evidence indicating that certain, appropriately ligated, coordinatively unsaturated, subnanometer M-4 transition-metal clusters can be relatively robust catalysts. Also demonstrated herein is that Rh4 clusters are poisoned by Hg(0), demonstrating for the first time that the classic Hg(0) poisoning test of "homogeneous" vs "heterogeneous" catalysts cannot distinguish Rh-4-based subnanometer catalysts from Rh(0)(n) nanoparticle catalysts, at least for the present examples of these two specific, Rh-based catalysts

Analysis of Oxygenated Compounds in Hydrotreated Biomass Fast Pyrolysis Oil Distillate Fractions

Three hydrotreated bio-oils with different oxygen contents (8.2, 4.9, and 0.4 w/w) were distilled to produce light, naphtha, jet, diesel, and gas oil boiling range fractions that were characterized for oxygen-containing species by a variety of analytical methods. The bio-oils were originally generated from lignocellulosic biomass in an entrained-flow fast pyrolysis reactor. Analyses included elemental composition, carbon type distribution by ¹³C nuclear magnetic resonance, acid number, gas chromatography/mass spectroscopy, volatile organic acids by liquid chromatography, and carbonyl compounds by 2,4-dinitrophenylhydrazine derivatization and liquid chromatography. Acid number titrations employed an improved titrant–electrode combination with faster response that allowed the detection of multiple end points in many samples and allowed for acid values attributable to carboxylic acids and to phenols to be distinguished. The results of these analyses showed that the highest oxygen content bio-oil fractions contained oxygen as carboxylic acids, carbonyls, aryl ethers, phenols, and alcohols. Carboxylic acids and carbonyl compounds detected in this sample were concentrated in the light, naphtha, and jet fractions (<260 °C boiling point). The carboxylic acid content of all of the high oxygen content fractions was likely too high for these materials to be considered as fuel blendstocks, although the potential for blending with crude oil or refinery intermediate streams may exist for the diesel and gas oil fractions. The 4.9% oxygen sample contained, almost exclusively, phenolic compounds found to be present throughout the boiling range fractions, which imparted measurable acidity primarily in the light, naphtha, and jet fractions. Additional study is required to understand what levels of the weakly acidic phenols could be tolerated in a refinery feedstock. The diesel and gas oil fractions from this upgraded oil had low acidity but still contained 3–4 wt % oxygen present as phenols that could not be specifically identified. These materials appear to have excellent potential as refinery feedstocks and some potential for blending into finished fuels. Fractions from the lowest oxygen-content oil exhibited some phenolic acidity but generally contained very low levels of oxygen functional groups. These materials would likely be suitable as refinery feedstocks and potentially as fuel blend components. Paraffins, isoparaffins, olefins, naphthenes, and aromatics (PIONA) analysis of the light and naphtha fractions showed benzene contents of 0.5 and 0.4 vol % and predicted (research octane number (RON) + motor octane number (MON))/2 of 63 and 70, respectively