Hydrogen partitioning as a function of time-on-stream for an unpromoted iron-based Fischer-Tropsch synthesis catalyst applied to CO hydrogenation

Sasol Ltd., the EPSRC (award reference EP/P505534/1), and the University of Glasgow are thanked for the provision of a postgraduate studentship (ALD). The STFC Rutherford Appleton Laboratory is thanked for access to neutron beam facilities. The Royal Society is thanked for the provision of an Industry Fellowship (PBW).Inelastic neutron scattering (INS) is employed to examine the evolution of a promoter-free iron-based Fischer-Tropsch synthesis catalyst (∼10 g catalyst charge) that is exposed to ambient pressure CO hydrogenation at 623 K for up to 10 days time-on-stream (T-o-S). The longer reaction time is selected to better understand how the formation of a previously described hydrocarbonaceous overlayer corresponds to the catalyst conditioning process. Although the onset of pseudo steady-state reactor performance is observed at approximately 9 h T-o-S, INS establishes that the intensity of the C-H stretching mode of the sp3-hybridized component of the hydrocarbonaceous overlayer saturates at about 24 h T-o-S, while the corresponding intensity of the C-H stretching mode of the sp2-hybridized component requires 100-200 h T-o-S to achieve saturation. This novel series of measurements reveal different aspects of the complex catalyst evolutionary process to be indirectly connected with catalytic turnover.Publisher PDFPeer reviewe

An inelastic neutron scattering investigation of the temporal behaviour of the hydrocarbonaceous overlayer of a prototype Fischer-Tropsch to olefins catalyst

Sasol Ltd., the University of Glasgow and the EPSRC [award reference EP/P505534/1] are thanked for the provision of a postgraduate studentship (ALD). The Royal Society is thanked for the provision of an Industry Fellowship (PBW).A dual sodium and sulfur promoted haematite, representative of a candidate Fischer-Tropsch to olefins (FTO) catalyst, is prepared and contrasted with the performance of an unpromoted hematite sample in the ambient pressure CO hydrogenation reaction at 623 K as a function of time-on-stream (0–24 h). In-situ post-reaction temperature-programmed oxidation measurements show the carbon evolutionary phase of the catalyst conditioning process to be retarded for the FTO catalyst. Ex-situ inelastic neutron scattering measurements show the promoters perturb the formation of a previously described hydrocarbonaceous overlayer. Specifically, whilst the sp3 hybridised C–H modes of the hydrocarbonaceous overlayer are almost unaffected by the additives, the formation of the overlayer’s sp2 hybridised C–H modes are noticeably impeded. The results are discussed in terms of the Na/S promoters disturbing the formation of an ordered hydrocarbonaceous overlayer that is thought to constrain the supply of adsorbed hydrogen atoms, which favours the formation of unsaturated hydrocarbons associated with the FTO process.Publisher PDFPeer reviewe

There Are Moments That Hang Suspended

This project is the culmination of ten years of work in poetry. It was begun in imitation of those who impressed, not only with their fine words and dexterity with language, but also with their clear conviction in their subject material. Reflected in the works of Allen Ginsberg, Walt Whitman, and Adrienne Rich, among others, was evidence of a life lived, in Thoreau\u27s term, deliberately. The writing of poetry seemed to be not simply a means of expression, but a goad to live a life worth examining, and to keep doing so; a progress report for a radical mind. Politics and poetry have always been connected, though at times the connection is difficult to locate. Overtly political poems often flop rather than booming; didactic, sentimental, tinny. If the connection between them is not found solely in the political poem, maybe it can be found in the conditions of the poem\u27s creation. Life is so often ineffable, betraying words and the minds that would use them. To write a poem, one must first be connected to life, using that connection to enliven inert language. The political journey of poetry is the management of that relationship, and the deliberate definition of its forms and avenues. The first and best tool in this process is attention. This includes attention to oneself, to the myriad entities, relationships, institutions and literatures surrounding the writer, and finally to the poem itself. If a poem is to stand as a piece of art, it is measured by its intentionality, by the evidence of its purposefulness. Though the situation that occasions a poem must be considered as given, the poem, as response, is in effect a series of choices. These choices are the essence of the poem itself, and they are moral choices. Which word to use, how to break a line, how to represent one\u27s perspective on the world, are choices which directly entangle the poet with their surroundings, with their language and literature, and with their reader. This sense of the primacy of a living relationship, of a poetry that knows it is in the world and cannot forget that fact, is perhaps the first choice. Then, in the words of Adrienne Rich, I hope you find here: not a map of choices but a map of variations/on the one great choice

Temporality and Intervention Effects: Latent Trajectory Analysis of a Homeless Mental Health Program

Intervention analyses which incorporate temporality over a followup period typically note differences in the patterns of "single-curves" for each the experimental and control groups or differences in temporally-based taxonomies between experimentals and controls. But the former fails to allow for the possibility of subgroups of multiple trajectories and the latter collapses time (e.g., average spell durations) and arbitrarily creates cut-points to form its taxonomies. This paper investigates the utility for intervention research of using latent class growth analysis (LCGA). This method incorporates the more complete temporal information used by single-curve approaches to statistically identify the multiple subgroups at the heart of the taxonomic approach. The authors do this by reanalyzing a critical time intervention study (CTI) of homeless mentally ill men that used both single-curve and taxonomic approaches. By finding, among other things, differences between experimentals and controls in the number, sizes and patterns of latent subgroups than were found in the prior analysis, this paper suggests the utility of LCGA for assessing service interventions

Capturing Intervention Effects Over Time: Reanalysis of a Critical Time Intervention for Homeless Mentally Ill Men

Objectives. We analyzed whether a method for identifying latent trajectories—latent class growth analysis (LCGA)—was useful for understanding outcomes for individuals subject to an intervention. Methods. We used LCGA to reanalyze data from a published study of mentally ill homeless men in a critical time intervention (CTI) program. In that study, 96 men leaving a shelter's onsite psychiatric program were randomly assigned to experimental and control groups. The former received CTI services and the latter usual services. Each individual's housing circumstances were observed for 18 months after program initiation. Our outcome measure was monthly homelessness: a person was considered homeless in a month if he was homeless for even 1 night that month. Results. Four latent classes were found among the control group, but just 3 among the experimental group. Control, but not experimental, group individuals showed a small class of chronically homeless men. The size of the never-homeless class was 19 percentage points larger for the experimental than for the control group. J- and inverted-U-shaped patterns were also found among both groups, but with important differences in timing of patterns. Conclusions. Our results reveal effects not apparent in the original analysis, suggesting that latent class growth models improve intervention evaluation

Welfare Research Perspectives: Past, Present, and Future, 2000 Edition

This is the second in a series of three working papers designed to examine what has been learned since the enactment of the Personal Responsibility and Work Opportunity Reconciliation Act (PRWORA) of 1996

The First Galaxies: Clues from Element Abundances

It has recently become possible to measure directly the abundances of several chemical elements in a variety of environments at redshifts up to z = 5. In this review I summarise the latest observations of Lyman break galaxies, damped Lyman alpha systems and the Lyman alpha forest with a view to uncovering any clues which these data may offer to the first episodes of star formation. The picture which is emerging is one where the universe at z = 3 already included many of the components of today's galaxies--even at these early times we see evidence for Populations I and II stars, while the `smoking gun' for Population III objects may be hidden in the chemical composition of the lowest density regions of the IGM, yet to be deciphered.Comment: 15 pages, LaTex, 8 Postscript Figures. To appear in the Philosophical Transactions of The Royal Society, Series