There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

CO2 conversion covers a wide range of possible application areas from fuels to bulk and commodity chemicals and even to specialty products with biological activity such as pharmaceuticals. In the present review, we discuss selected examples in these areas in a combined analysis of the state-of-the-art of synthetic methodologies and processes with their life cycle assessment. Thereby, we attempted to assess the potential to reduce the environmental footprint in these application fields relative to the current petrochemical value chain. This analysis and discussion differs significantly from a viewpoint on CO2 utilization as a measure for global CO2 mitigation. Whereas the latter focuses on reducing the end-of-pipe problem “CO2 emissions” from todays’ industries, the approach taken here tries to identify opportunities by exploiting a novel feedstock that avoids the utilization of fossil resource in transition toward more sustainable future production. Thus, the motivation to develop CO2-based chemistry does...

Sustainable Conversion of Carbon Dioxide: An Integrated Review of Catalysis and Life Cycle Assessment

Despite being first demonstrated over 160 years ago, and offering significant environmental benefits and high electrical efficiency, it is only in the last two decades that fuel cells have offered a realistic prospect of being commercially viable. The solid oxide fuel cell (SOFC) offers great promise and is presently the subject of intense research activity. Unlike other fuel cells the SOFC is a solid-state device which operates at elevated temperatures. This review discusses the particular issues facing the development of a high temperature solid-state fuel cell and the inorganic materials currently used and under investigation for such cells, together with the problems associated with operating SOFCs on practical hydrocarbon fuels.

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Solid oxide fuel cells

A study is conducted to demonstrate catalytic dehydrogenation of light alkanes on metals and metal oxides. The study provides a complete overview of the materials used to catalyze this reaction, as dehydrogenation for the production of light olefins has become extremely relevant. Relevant factors, such as the specific nature of the active sites, as well as the effect of support, promoters, and reaction feed on catalyst performance and lifetime, are discussed for each catalytic Material. The study compares different catalysts in terms of the reaction mechanism and deactivation pathways and catalytic performance. The duration of the dehydrogenation step depends on the heat content of the catalyst bed, which decreases rapidly due to the endothermic nature of the reaction. Part of the heat required for the reaction is introduced to the reactors by preheating the reaction feed, additional heat being provided by adjacent reactors that are regenerating the coked catalysts.

Catalytic dehydrogenation of light alkanes on metals and metal oxides.

Almost CO-free hydrogen gas, which could be directly used as a feed for a PEM fuel cell, can be produced by a novel steam reforming process of methane in a fixed bed reactor which contains two different catalysts layers which go through a periodic reduction/re-oxidation cycle. During the reduction phase, water-free methane is converted at the first layer (Pt–Ce0.5Zr0.5O2) into a mixture of СО and Н2 by partial oxidation. This mixture is fed directly to a second layer of Fe2O3–Ce0.5Zr0.5O2 where the products of the methane partial oxidation reduce the iron-containing catalyst whereby giving CO2 and H2O. During the re-oxidation phase of the cycle, the two-layer reactor is fed with pure steam which is converted into a CO-free hydrogen gas whereby leading to the re-oxidation of the catalytic materials in both layers so that that they can be reused in the next redox cycle. The present study reports the preparation and characterization of suitable catalytic materials, related activity tests and kinetic studies which demonstrate the feasibility of the proposed process concept.

Hydrogen production from methane by steam reforming in a periodically operated two-layer catalytic reactor

Effective integration of CO2 capture and its conversion is an attractive strategy to reduce the anthropogenic CO2 emissions meanwhile achieve the potential revenue of CO2 molecule. Calcium-looping dry reforming of methane (CaLDRM) has emerged as such a promising process, implemented over a bifunctional reactor combining a CaO-based sorbent and a Ni-based catalyst, to achieve CO2 capture and in-situ conversion with CH4 into syngas. Herein, we synthesize a bifunctional Ni-Ca based material, i.e. Ni and CeO2 nanoparticles co-loaded on ZrO2-coated CaCO3, which enables isothermal capture and release of CO2 at the temperature favorable for DRM reaction, allowing to operate CaLDRM process in a single reactor by simple gas switching. Thanks to the stabilization effect of the ZrO2 layer, both CaO and Ni particles are exempted from severe sintering, maintaining the activity of capture and catalysis. The addition of CeO2 contributes not only to combat the accumulation of inactive carbon during long-term DRM but also to activate CO2 and CH4, accordingly enhancing syngas production, during cyclic CaLDRM. Importantly, the bifunctional material can succesfully drive CaLDRM cycles, converting over 40 % of CH4 and CO2, under 5 vol% CO2 feed concentration (as low as real flue gas) at 720 °C, which is a thermodynamically extremely unfavorable condition (equilibrium conversion below 3 %).

Bifunctional Ni-Ca based material for integrated CO2 capture and conversion via calcium-looping dry reforming

A detailed study of new oxygen carrier materials, Mg–Fe–Al–O, with various loadings of iron oxide (10–100 wt% Fe2O3) is carried out in order to investigate the relationship between material transformation, stability and CO yield from CO2 conversion. In situ XRD during H2-TPR, CO2-TPO and isothermal chemical looping cycles as well as Mossbauer spectroscopy are employed. All samples show the formation of a spinel phase, MgFeAlOx. High loadings of iron oxide (50–90 wt%) lead to both spinel and Fe2O3 phases and show deactivation in cycling as a result of Fe2O3 particle sintering. During the reduction, reoxidation and cycling of the spinel MgFeAlOx phase, only limited sintering occurs. This is evidenced by the stable spinel crystallite sizes (∼15–20 nm) during isothermal cycling. The reduction of MgFe3+AlOx starts at 400 °C and proceeds via partial reduction to MgFe2+AlOx. Prolonged cycling and higher temperatures (>750 °C) lead to deeper reduction and segregation of Fe from the spinel structure. Very high stability and CO yield from CO2 conversion are found in Mg–Fe–Al–O materials with 10 wt% Fe2O3, i.e. the lowest oxygen storage capacity among the tested samples. Compared to 10 wt% Fe2O3 supported on Al2O3 or MgO, the CO yield of the 10 wt% Fe2O3–MgFeAlOx spinel is ten times higher.

Mg–Fe–Al–O for advanced CO2 to CO conversion: carbon monoxide yield vs. oxygen storage capacity

The role of CO2 in the dehydrogenation of propane over WOx-VOx/SiO2

A bifunctional 9 wt.%NiO-16 wt.%Fe 2 O 3 /MgAl 2 O 4 material was prepared for CO 2 conversion to CO by auto-thermal catalyst-assisted chemical looping. This process is designed to maximize CO 2 conversion. The generation of CO from CO 2 was investigated between 873 K and 1023 K. The high endothermicity of methane dry reforming and the material deactivation by coke deposition were avoided by the simultaneous feeding of CH 4 , CO 2 and O 2 in a 1:1:0.5 molar ratio during the reduction half-cycle of chemical looping. In this half-cycle, interaction of Ni with Fe leads to Ni-Fe alloy formation. The resulting Ni-based catalyst converts CH 4  + CO 2  + O 2 into a mixture of CO and H 2 , which both reduce Fe 3 O 4 , producing CO 2 and H 2 O. In the CO 2 re-oxidation half-cycle, CO is produced and the Ni-Fe alloy decomposes into Ni and Fe 3 O 4 . The reduction capacity ( R c ) of the gas mixture strongly depends on the ratio R c between reducing and oxidizing gases. Based on thermodynamic calculations, high conversion of Fe 3 O 4 to reduced state can be reached if R c  > 2 and T > 873 K. During prolonged auto-thermal chemical looping at 1023 K, the 9 wt.%NiO–16 wt.%Fe 2 O 3 /MgAl 2 O 4 suffers from deactivation in the first five cycles, after which a more stable operation is established. Based on TEM measurements, sintering was found to be the main cause for the initial decrease of CO production.

Vladimir Galvita

Papers

Hydrogen production from methane by steam reforming in a periodically operated two-layer catalytic reactor

Bifunctional Ni-Ca based material for integrated CO2 capture and conversion via calcium-looping dry reforming

Mg–Fe–Al–O for advanced CO2 to CO conversion: carbon monoxide yield vs. oxygen storage capacity

The role of CO2 in the dehydrogenation of propane over WOx-VOx/SiO2

CO2 conversion to CO by auto-thermal catalyst-assisted chemical looping