James Robert Warner

Kinetic Stability of MOF-5 in Humid Environments: Impact of Powder Densification, Humidity Level, and Exposure Time

Metal-organic frameworks (MOFs) are an emerging class of microporous, crystalline materials with potential applications in the capture, storage, and separation of gases. Of the many known MOFs, MOF-5 has attracted considerable attention because of its ability to store gaseous fuels at low pressure with high densities. Nevertheless, MOF-5 and several other MOFs exhibit limited stability upon exposure to reactive species such as water. The present study quantifies the impact of humid air exposure on the properties of MOF-5 as a function of exposure time, humidity level, and morphology (i.e., powders vs pellets). Properties examined include hydrogen storage capacity, surface area, and crystallinity. Water adsorption/desorption isotherms are measured using a gravimetric technique; the first uptake exhibits a type V isotherm with a sudden increase in uptake at ∼50% relative humidity. For humidity levels below this threshold only minor degradation is observed for exposure times up to several hours, suggesting that MOF-5 is more stable than generally assumed under moderately humid conditions. In contrast, irreversible degradation occurs in a matter of minutes for exposures above the 50% threshold. Fourier transform infrared spectroscopy indicates that molecular and/or dissociated water is inserted into the skeletal framework after long exposure times. Densification into pellets can slow the degradation of MOF-5 significantly, and may present a pathway to enhance the stability of some MOFs.

Nitrous oxide emissions from a medium-duty diesel truck exhaust system

Starting in 2010, medium-duty diesel trucks in the USA were introduced with aftertreatment systems that contained precious metal oxidation catalysts, soot filters, and selective catalytic reduction (SCR) systems for control of nitrogen oxides (NO, NO2). While modern diesel aftertreatment systems have high performance for meeting hydrocarbons, carbon monoxide (CO), NOx, and particulate matter, there is some concern over emission of nitrous oxide (N2O) that can be formed within the exhaust system. N2O has an atmospheric lifetime of approximately 114 years and is 298 times more effective than CO2 at trapping heat in the atmosphere. In this study, the sources of N2O were compared in the laboratory flow reactor and at the system level on diesel trucks. The interactions of HC with NOx on the DOC and NOx with NH3 within the SCR catalyst were the predominant mechanisms for N2O formation. The composite N2O mass emission was calculated to be approximately 43 mg/mi, resulting in an equivalent CO2 penalty of about 2%, similar to the 1% to 3% penalty estimated for the global light-duty vehicle fleet.

The Effect of Ash Accumulation on Gasoline Particulate Filters: A Comparison Between Laboratory and Field Aged Samples

Stringent regulations worldwide will limit the level of particulate matter (PM) and particle number (PN) emitted from gasoline engines. Gasoline particulate filters (GPFs) present one strategy for meeting PM and PN limits over the full operating range of the engine. Over time these filters accumulate incombustible ash, increasing system pressure drop and adversely effecting engine performance. The effect of aging as a result of ash accumulation is examined over the full lifetime of gasoline particulate filters, using a novel accelerated aging system. This system utilizes a gasoline combustion chamber into which lubricating oil is injected simulating combustion in the cylinder — the primary source of ash. This report details the construction and validation of this system.Copyright