Dialing in single-site reactivity of a supported calixarene-protected tetrairidium cluster catalyst.

A closed Ir4 carbonyl cluster, 1, comprising a tetrahedral metal frame and three sterically bulky tert-butyl-calix[4]arene(OPr)3(OCH2PPh2) (Ph = phenyl; Pr = propyl) ligands at the basal plane, was characterized with variable-temperature 13C NMR spectroscopy, which show the absence of scrambling of the CO ligands at temperatures up to 313 K. This demonstration of distinct sites for the CO ligands was found to extend to the reactivity and catalytic properties, as shown by selective decarbonylation in a reaction with trimethylamine N-oxide (TMAO) as an oxidant, which, reacting in the presence of ethylene, leads to the selective bonding of an ethyl ligand at the apical Ir site. These clusters were supported intact on porous silica and found to catalyze ethylene hydrogenation, and a comparison of the kinetics of the single-hydrogenation reaction and steady-state hydrogenation catalysis demonstrates a unique single-site catalyst-with each site having the same catalytic activity. Reaction orders in the catalytic ethylene hydrogenation reaction of approximately 1/2 and 0 for H2 and C2H4, respectively, nearly match those for conventional noble-metal catalysts. In contrast to oxidative decarbonylation, thermal desorption of CO from silica-supported cluster 1 occurred exclusively at the basal plane, giving rise to sites that do not react with ethylene and are catalytically inactive for ethylene hydrogenation. The evidence of distinctive sites on the cluster catalyst leads to a model that links to hydrogen-transfer catalysis on metals-involving some surface sites that bond to both hydrocarbon and hydrogen and are catalytically engaged (so-called "*" sites) and others, at the basal plane, which bond hydrogen and CO but not hydrocarbon and are reservoir sites (so-called "S" sites)

Grasshopper Outlook on Rangelands: 2011

Grasshoppers are often found to be a significant problem for both farmers and ranchers. Even though grasshoppers are a normal component of a forage ecosystem and generally exert minimal disturbance, problems occur when conditions lead to grasshop¬per populations that increase to the point where they cause millions of dollars of damage. Grasshopper outbreaks are the result of a complex combination of factors. Several factors are beyond the control of managers. However, the “pasture microcli¬mate” (the immediate environment where grasshop¬pers hatch, grow, and reproduce) may be subject to subtle manipulation. Because grasshopper outbreaks are progressive and cumulative, small interruptions or reductions in the rates of metabolic processes may serve to reduce population expansion and consequent damage to vegetation. Spring weather plays a key role in the severity of outbreaks. Warm temperatures with little rainfall are favorable for the hatching and development of grasshoppers, while cool and wet conditions follow¬ing hatch are unfavorable to grasshopper growth and development. Surveyed grasshopper populations for 2010 are shown in fig. 1

Ammonia Emissions from U.S. Laying Hen Houses in Iowa and Pennsylvania

Ammonia (NH3) emission rates (ER) of ten commercial layer houses (six high-rise or HR houses and four manure- belt or MB houses) with different manure handling or dietary schemes were monitored for one year in Iowa (IA) and Pennsylvania (PA). Gaseous (NH3 and CO2) concentrations of incoming and exhaust air streams were measured using custom-designed portable monitoring units that shared similar performance to EPA-approved measurement apparatus. Building ventilation rates were determined by calibrated CO2 mass balance using the latest metabolic rate data for modern laying hens. The field monitoring involved a total of 386 and 164 house-day measurements or 18,528 and 7,872 30-min emission data points for the HR houses and the MB houses, respectively. The ER showed considerable diurnal and seasonal variations. The annual mean ERs (g NH3 hen-1 d-1) and standard errors were 0.90 ±0.027 for IA-HR houses with standard diet, 0.81 ±0.02 for IA-HR houses with a nutritionally balanced 1% lower crude protein diet, 0.83 ±0.070 for PA-HR houses with standard diet, 0.054 ±0.0035 for IA-MB houses with daily manure removal, and 0.094 ±0.006 for PA-MB houses with twice a week manure removal. Mass balance of nitrogen (N) intake and output performed for IA-HR houses revealed a total N intake recovery of 94% to 101%, further verifying the certainty of the NH3 ER measurements. Results of the study contribute to the U.S. national inventory on NH3 emissions from animal feeding operations, particularly laying hen facilities as affected by housing type, manure handling scheme, crude protein content of the diet, and geographical location

Involving Students in a Collaborative Project To Help Discover Inexpensive, Stable Materials for Solar Photoelectrolysis

In general, laboratory experiments focus on traditional chemical disciplines. While this approach allows students the ability to learn and explore fundamental concepts in a specific area, it does not always encourage students to explore interdisciplinary science. Often little transfer of knowledge from one area to another is observed, as students are given step-by-step instructions on how to complete their task with little involvement or problem solving. Herein, we provide an example of a real-time research laboratory experiment that is aimed at individual’s exploration and development, with the scientific goal of discovering inexpensive, stable oxide semiconductors that can efficiently photoelectrolyze water to a useable fuel, hydrogen. Students create unique metal oxide semiconductors combinations, scan the samples for photoactivity using a purchased scan station, and report their findings to a collaborative database. A distinctive feature of the project is its ability to be implemented in a variety of educational levels with a breadth and depth of material covered accordingly. Currently, kits are being used in secondary education classrooms, at undergraduate institutions, or as outreach activities. The project provides students and scientists from different disciplines the opportunity to collaborate in research pertaining to clean energy and the global energy crisis

Iridium Complexes and Clusters in Dealuminated Zeolite HY: Distribution between Crystalline and Impurity Amorphous Regions

Dealuminated zeolite HY was used to support Ir(CO)_2 complexes formed from Ir(CO)_2(C_5H_7O_2). Infrared and X-ray absorption spectra and atomic resolution electron microscopy images identify these complexes, and the images and ^(27)Al NMR spectra identify impurity amorphous regions in the zeolite where the iridium is more susceptible to aggregation than in the crystalline regions. The results indicate the value of electron microscopy in characterizing the amorphous impurity regions of zeolites and a significant stability limitation of metals in these regions of zeolite catalyst supports