Performance of silica-supported copper oxide sorbents for SOx/NOx-removal from flue gas II. Selective catalytic reduction of nitric oxide by ammonia

The selective catalytic reduction (SCR) of nitric oxide by ammonia was studied for silica-supported copper oxide particles to be used as a sorbent/catalyst in a continuous process for the simultaneous removal of SOx and NOx from flue gases. The SCR-behaviour was determined as a function of the sulphation degree, i.e. the fraction of copper oxide converted to copper sulphate, at temperatures ranging from 20 to 450°C. Up to 350°C, the fresh catalyst with 0% CuSO4 showed a high selectivity towards production of nitrogen and water by the reaction of nitric oxide with ammonia and oxygen. At higher temperature, nitric oxide removal efficiencies decreased due to the oxidation of ammonia by oxygen. With an increase of the sulphation degree, the maximum temperature for selective catalytic reduction of nitric oxide gradually increased up to 420°C for a sulphation degree of 80%. In addition, the maximum nitric oxide removal efficiency increased as well. After regeneration of catalyst particles with a sulphation degree of 80%, realised by reduction with hydrogen and subsequent re-oxidation, the catalytic behaviour was similar to that of fresh catalyst particles with a sulphation degree of 5%. This is ascribed to the formation of some Cu2S during the reduction, which is oxidised to CuSO4 in the subsequent oxidation step. Since the selectivity towards the reduction of nitric oxide with ammonia is maintained up to about 375°C, a temperature which is very suitable for SOx removal as well, the silica-supported CuO investigated can be applied as a sorbent/catalyst for the simultaneous removal of SOx and NOx from flue gases. The reaction rate constants for SOx and NOx removal appeared to be of the same order of magnitude provided that the reduced sorbent/catalyst enters the absorber directly, i.e. without a separate pre-oxidation

New Measurements with Stopped Particles at the LHC

Metastable particles are common in many models of new physics at the TeV scale. If charged or colored, a reasonable fraction of all such particles produced at the LHC will stop in the detectors and give observable out of time decays. We demonstrate that significant information may be learned from such decays about the properties (e.g. charge or spin) of this particle and of any other particles to which it decays, for example a dark matter candidate. We discuss strategies for measuring the type of decay (two- vs three-body), the types of particles produced, and the angular distribution of the produced particles using the LHC detectors. We demonstrate that with O(10-100) observed decay events, not only can the properties of the new particles be measured but indeed even the Lorentz structure of the decay operator can be distinguished in the case of three-body decays. These measurements can not only reveal the correct model of new physics at the TeV scale, but also give information on physics giving rise to the decay at energy scales far above those the LHC can probe directly.Comment: 31 pages, 6 figures. References added, updated to reflect recent experimental results, version accepted for publication in Physical Review

Performance of silica-supported copper oxide sorbents for SO@#x@#/NO@#x@#-removal from flue gas I. Sulphur dioxide absorption and regeneration kinetics

Sulphur dioxide absorption and regeneration kinetics of several silica-supported copper oxide (CuO) sorbents were studied in a microbalance over a temperature range of 300 to 450°C. The porous silica support was prepared according to a sol-gel technique, and CuO was deposited on this support through an ion-exchange technique to achieve a uniform, highly dispersed CuO deposition. During up to 75 cycles of oxidation, sulphation, and reduction, the ion-exchanged sorbents did not show a significant loss in chemical activity except for some deactivation in the first 1¿3 cycles. The sulphation kinetics of the pre-oxidised ion-exchanged sorbents were found to be in agreement with literature data for impregnated alumina-supported CuO sorbents. In case of direct contact of reduced ion-exchanged sorbents with simulated flue gas, the simultaneous and fast oxidation was determined to have a large positive effect on the sulphation rate up to approximately 60% conversion to copper sulphate. This was mainly attributed to structural effects inside the CuO deposits. For the sulphated ion-exchanged sorbents, the reduction by hydrogen was identified as an autocatalytic reaction. The autocatalytic effect was also observed during the (much slower) reduction by methane, but there it was preceded by a period in which a second autocatalytic effect appeared. The reaction kinetics of the ion-exchanged sorbents developed were furthermore compared with experimental results of other silica-supported CuO sorbents prepared by vacuum impregnation and homogeneous deposition-precipitation

Mass transfer between gas and particles in a gas-solid trickle flow reactor

Gas-solids mass transfer was studied for counter-current flow of gas and millimetre-sized solid particles over an inert packing at dilute phase or trickle flow conditions. Experimental data were obtained from the adsorption of water vapour on 640 and 2200 ¿m diameter molecular sieve spheres at ambient conditions in a test column with a cross-sectional area of 0.06 x 0.06 m2 and a packing height of 0.27 or 0.53 m. The packing consisted of a bank of regularly stacked, 0.01 m diameter bars made of stainless steel. Assuming the effective area for mass transfer to be equal to the external surface area of the spheres, the experimental values of the average gas¿solids mass transfer coefficient were determined to amount to approximately 40¿80% of the values calculated from the well-known Ranz¿Marshall correlation for a single sphere in an undisturbed gas flow. These experimental values were identified as conservative estimates of the actual average gas¿solids mass transfer coefficient because the pore diffusion resistance could not be eliminated completely. A comparison between experimental data on hydrodynamics (gas¿solids momentum transfer) and gas¿solids mass transfer indicated, furthermore, that the influence of particle shielding with interfering concentration boundary layers of different particles was small for the millimetre-sized particles and the experimental conditions investigated. Gas¿solids mass transfer as well as gas¿solids momentum transfer were mainly determined by single-particle flow behaviour

Statutes and Democratic Self-Authorship

In this Article, we argue that both sides of the usual debate over statutory interpretation—text versus purpose—rest on a common, but flawed, premise. Judges and scholars have assumed that legislative bodies are the authors of statutes. We disagree; instead, we argue that the people are the authors of statutes. Legislative bodies play an indispensable role in the process: they draft statutes. And courts play a similarly indispensable role: they interpret statutes. But ultimately, it is the polity—we, the people—that is responsible, as authors, for the content of the law. This shift yields dramatic consequences. To date, no theory of statutory interpretation has been able to explain the actual labor of interpreting statutes—either with respect to “super” statutes or with respect to regular statutes. Canons of statutory construction, though familiar to any practitioner, are a source of puzzlement for theorists. Our theory attempts to answer the challenge. It both offers an explanation of existing interpretive practices and supplies a normatively compelling view of what statutory construction involves. In this effort, we reach back to the origins of modern political theory—to the work of Thomas Hobbes—to demonstrate that “self-authorship” has long been integral to the ideal of democracy. Ultimately, the problem is very simple. Commentators have long been sympathetic to the notion of self-authorship as applied to “fundamental” law—especially constitutional law. But they have failed to notice that the exact same issues are at stake in the construction of “ordinary” laws. That is the connection we make here

Image potential states at transition metal oxide surfaces: A time-resolved two-photon photoemission study on ultrathin NiO films

For well-ordered ultrathin films of NiO(001) on Ag(001), a series of unoccupied states below the vacuum level has been found. The states show a nearly free electron dispersion and binding energies which are typical for image potential states. By time-resolved two-photon photoemission (2PPE), the lifetimes of the first three states and their dependence on oxide film thickness are determined. For NiO film thicknesses between 2 and 4 monolayers (ML), the lifetime of the first state is in the range of 28–42 fs and shows an oscillatory behavior with increasing thickness. The values for the second state decrease monotonically from 88 fs for 2 ML to 33 fs for 4 ML. These differences are discussed in terms of coupling of the unoccupied states to the layer-dependent electronic structure of the growing NiO film