Moderate Conversion Research Articles

CD40 agonist converting CTL exhaustion via the activation of the mTORC1 pathway enhances PD-1 antagonist action in rescuing exhausted CTLs in chronic infection

Expansion of PD-1-expressing CD8+ cytotoxic T lymphocytes (CTLs) and associated CTL exhaustion are chief issues for ineffective virus-elimination in chronic infectious diseases. PD-1 blockade using antagonistic anti-PD-L1 antibodies results in a moderate conversion of CTL exhaustion. We previously demonstrated that CD40L signaling of ovalbumin (OVA)-specific vaccine, OVA-Texo, converts CTL exhaustion via the activation of the mTORC1 pathway in OVA-expressing adenovirus (AdVova)-infected B6 mice showing CTL inflation and exhaustion. Here, we developed AdVova-infected B6 and transgenic CD11c-DTR (termed AdVova-B6 and AdVova-CD11c-DTR) mice with chronic infection, and assessed a potential effect of CD40 agonist on the conversion of CTL exhaustion and on a potential enhancement of PD-1 antagonist action in rescuing exhausted CTLs in our chronic infection models. We demonstrate that a single dose of anti-CD40 alone can effectively convert CTL exhaustion by activating the mTORC1 pathway, leading to CTL proliferation, up-regulation of an effector-cytokine IFN-γ and the cytolytic effect in AdVova-B6 mice. Using anti-CD4 antibody and diphtheria toxin (DT) to deplete CD4+ T-cells and dendritic cells (DCs), we discovered that the CD40 agonist-induced conversion in AdVova-B6 and AdVova-CD11c-DTR mice is dependent upon host CD4+ T-cell and DC involvements. Moreover, CD40 agonist significantly enhances PD-1 antagonist effectiveness in rescuing exhausted CTLs in chronic infection. Taken together, our data demonstrate the importance of CD40 signaling in the conversion of CTL exhaustion and its ability to enhance PD-1 antagonist action in rescuing exhausted CTLs in chronic infection. Therefore, our findings may positively impact the design of new therapeutic strategies for chronic infectious diseases.

Current Status, Threats and Conservation Needs of The Endemic Cycas wadei Merrill

The population size and structure of Cycas wadei were assessed along with habitat traits to update the current level of knowledge for conserving this Critically Endangered endemic species. Direct measurements of plant density and size, chemical analyses of soil and leaf tissue samples, and surveys of sympatric plants were conducted. The adult population was calculated at 5,051, indicating historical population size estimates were inaccurately low. Highest densities in forested fragments were 800 plants per hectare, with adults comprising 34% of the population. Density in grasslands was as high as 1,100 plants per hectare, with adults comprising 31% of the population. The dominant grass was Themeda gigantea (Cav.) Hackel, not Imperata as previously reported. The prediction that the soils were ultramafic was rejected but opinions that the soils were extremely infertile were confirmed by soil analyses. Leaf stoichiometry revealed the cycad plants were primarily limited by potassium availability and secondarily limited by phosphorus availability. Habitat conversion is the acute threat that must be monitored in the near future, and an attempt to moderate or halt this conversion is the greatest conservation need. Poaching is a second threat that has not been acute to date, but has the potential to become a greater threat if the remote habitat becomes more connected to national trade routes. Fire damage is the third major threat, and has the potential to become a greater threat if historical fire frequency is altered

Total Ionizing Dose Effects on a 12-bit 40kS/s SAR ADC Designed With a Dummy Gate-Assisted n-MOSFET

A 12-bit 40kS/s successive approximation register analog-to-digital converter (ADC) designed with a dummy gate-assisted (DGA) n-MOSFET is presented for space applications requiring high resolution, low power consumption, and moderate conversion speed. Additionally, a custom-designed metal finger capacitor and a body-tied p-MOSFET protected by guard ring in a bootstrapping circuit were used to mitigate the performance degradation caused by radiation-induced leakage current. The designed ADC was fabricated in a commercial standard 0.35 $\mu {\mathrm { m}}$ CMOS process. In order to evaluate its radiation hardness, the fabricated ADC was exposed to 60Co gamma rays with a dose of up to 300krad (Si). The measured signal-to-noise-and-distortion ratio (SNDR) and spurious-free dynamic range (SFDR) were 67.9dB and 78.7dB, respectively. Although a small amount of degradation of the SNDR was observed after radiation exposure, it corresponds to only about a 0.1 effective-number-of-bit (ENOB) drop from the measured result of an unirradiated chip.

Synthesis, characterization and photovoltaic properties of dithienobenzodithiophene-based conjugated polymers

Two new donor-acceptor typed conjugated polymers (P1 and P2) based on the large coplanar and more-extended donor dithieno[2,3-d:2,3-d′]benzo[1,2-b:4,5-b′]dithiphene and thienopyrroledione (TPD) units were synthesized. P1 and P2 have the same polymer backbone, but with different side chains, where P1 has 2-ethylhexyl side chains and P2 has the longer branched 4-ethyoctyl side chains. The solubility measurements show that P2 with longer branched 4-ethyloctyl side chain has better solubility in organic solvents than that of P1. The optical, electrochemical and photovoltaic properties were investigated. P1 and P2 show the very same absorption features in both solution and film states indicating an enhanced molecular planarity of the polymer chains in P1 and P2, which benefits from the large coplanar dithieno[2,3-d:2,3-d′]benzo[1,2-b:4,5-b′]dithiphene unit. The band-gaps of P1 and P2 are at 1.83 eV and 1.74 eV, respectively. The solar cells with P1 or P2 as the electron donor component and PC71BM as the electron acceptor were fabricated and measured under AM 1.5G illumination at 100 mW cm−2. The results show that the P2/PC71BM-based device showed a moderate power conversion efficiency of 2.86%, which is ∼50% improvement in comparison with P1/PC71BM-based device.

Biodiesel Production from <i>Sterculia foetida</i> Oil by Using Solid Support Catalyst

In the present work, the properties of bioester from Samrong oil (Sterculia Foetida) and characteristics of cellulose solid catalyst are described. Heterogeneous catalyst was prepared via carbonization, sulfonation and purification giving solid catalyst as brown powder. Control parameters were time and temperature of carbonization and sulfonation reaction, ratio of sulfuric acid to solid material and weight of solid material. The optimized carbonization condition was 300 °C for 15 h. The sulfonation temperature was 150 oC for 18 h under N2 producing 7.99 mmol/g of acid concentration on solid catalyst. The acidity in water of solid catalyst after purification and drying was decreasing. The results of biodiesel production showed that the triglyceride could be converted to biodiesel directly by one-step sulfonic acid catalyzed process. The experimental condition of reaction process was 3.0 M of catalyst concentration with 9:1 M ratio of methanol to triglyceride at the temperature of 80 °C. This catalysts provided high reactivity of transesterification. The present procedure represents a simple method for biodiesel production with a short reaction time and with moderate conversion rate.

Investigation of Fluorination on Donor Moiety of Donor-Acceptor 4,7-Dithienylbenzothiadiazole-Based Conjugated Polymers toward Enhanced Photovoltaic Efficiency.

It is known that fluorination on π-conjugated donor-acceptor (D-A) polymers can significantly affect the optoelectronic properties and fluorination on A moiety has been well established for design of efficient photovoltaic materials. For example, polymers based on 4,7-dithienyl-5,6-difluorobenzothiadiazole (DTffBT) have been intensively investigated and exhibited excellent performance, but the corresponding DTBT-based polymers without fluorine often display an unfavorable efficiency. With the purpose of improving photovoltaic efficiency of DTBT-based D-A polymers, we design three polymers PDTBT-TxfBT (x = 0, 1, 2) with fluorination on D moiety (TxfBT) and systematically investigate fluorination on the photophysical/electrochemical and photovoltaic properties. The results show that polymer solar cells (PSCs) based on PDTBT-TBT exhibit moderate power conversion efficiency (PCE) of 5.84%. However, the bis-fluorination on TffBT moiety (PDTBT-TffBT) can greatly enhance the molecular planarity and intermolecular interaction, improve the charge transport and heterojunction morphology, and further suppress the charge recombination losses. PSCs based on PDTBT-TffBT demonstrate obviously improved photovoltaic efficiency with the best PCE up to 7.53% without any processing additives, which ranks among the top DTBT-based PSCs. However, it should be noted that unsymmetrical fluorination on TfBT moiety (PDTBT-TfBT) impairs the regularity of polymer backbone and intermolecular interaction, increases the recombination losses, and seriously reduces the short-circuit current density and efficiency (5.44%). The results exhibit that fluorination on D moiety is a helpful strategy for design high-performance photovoltaic materials and the regularity of fluorination is crucial to improving efficiencies.

Atomic Layer Deposited Metal Oxides Films for Solar Cells

Direct utilization of sunlight into electrical power is of great interest as a clean and safe energy source. Among various types of solar cells, Si-based solar cells can yield high power conversion efficiency and thus, is in mass production for practical usage. However, the expensive fabrication cost of the Si-based solar cells stimulated a research for alternative types of solar cells. Dye-sensitized solar cells (DSSCs) and polymer solar cell (PSC) are considered as the promising candidates for the partial replacement of Si-based solar cell due to its advantages of low cost, easy fabrication, and moderate power conversion efficiency compared Si-based solar cells. Here, the effect of atomic layer deposited (ALD)-metal oxides thin films on the device performance of DSSC and PSC will be presented.

Reversible Deactivation Radical Polymerization of Monomers Containing Activated Aziridine Groups.

Polymers bearing activated aziridine groups are attractive precursors to α-substituted-β-amino-functionalized materials due to the enhanced reactivity of the pendant aziridine functionalities toward ring-opening by nucleophiles. Two aziridine-containing styrenic monomers, 2-(4-vinylphenyl)aziridine (VPA) and N-mesyl-2-(4-vinylphenyl)aziridine (NMVPA), were polymerized under a variety of reversible deactivation radical polymerization conditions. Low-catalyst-concentration atom transfer radical polymerization (LCC-ATRP) and reversible addition-fragmentation chain-transfer (RAFT) polymerization were ineffective at producing well-defined polymers from VPA due to side reactions between the aziridine functionalities and the agents controlling the polymerizations (catalysts or chain transfer agents). PolyVPA produced under nitroxide-mediated polymerization (NMP) conditions had narrow molecular weight distribution at low to moderate conversions of monomer, but branched and eventually cross-linked polymers were formed at higher conversions due to ring-opening reactions of the aziridine groups. Most of these undesirable side reactions were eliminated by attaching a methanesulfonyl (mesyl) group to the aziridine nitrogen atom, and well-defined linear homopolymers with targeted molecular weights were realized from NMVPA under RAFT and NMP conditions; however, side reactions between the aziridine groups and the catalyst in LCC-ATRP still occured and the polymerization was uncontrolled using this technique.

Bulk Free Radical Polymerization of Methyl Methacrylate and Vinyl Acetate: A Comparative Study

The model and methodology for estimating diffusion‐controlled rate coefficients for the methyl methacrylate (MMA) polymerization system is extended to the vinyl acetate (VAc) case. Comparison of the kinetic behavior and termination rate coefficients (kt) of both monomers suggests that at low conversions the termination reaction is controlled by the chemical step, whereas at moderate and high conversions it is controlled by the diffusive step which in turn is determined by the segmental diffusion of the long radicals and not by the center of mass diffusion of short radicals. It is found that, for most of the conversion range, diffusion coefficient for VAc is lower than the one for MMA notwithstanding that ktVAc > ktMMA. An explanation of this apparent inconsistency on the base of the model results and in terms of segmental mobility is proposed. image

Amidophosphine‐stabilized palladium complexes catalyse Suzuki–Miyaura cross‐couplings in aqueous media

We report a simple and efficient procedure for Suzuki–Miyaura reactions in aqueous media catalysed by amidophosphine‐stabilized palladium complexes trans‐{L3PPh2}2PdCl2 (3), trans‐{L3PPhtBu}2PdCl2 (4), [Pd(η3‐C3H5)(L3PPh2)Cl] (5) and {Pd[2‐(Me2NCH2)C6H4](L3PPh2)Cl} (6). The acidity of the NH proton in complexes 3, 4, 5, 6 plays an important role in their catalytic activity. In addition, the palladium complexes cis‐{L1PPh2}PdCl2 (1) and trans‐{L2PPh2}2PdCl2 (2) stabilized by phosphines containing Y,C,Y‐chelating ligands L1,2 have also been found to be useful catalysts for Suzuki–Miyaura reactions in aqueous media. The method can be effectively applied to both activated and deactivated aryl bromides yielding high or moderate conversions. The catalytic activity of couplings performed in pure water increases when utilizing a Pd complex with more acidic NH protons. A decrease of palladium concentration from 1.0 to 0.5 mol% does not lead to a substantial loss of conversion. In addition, Pd complex 1 can be efficiently recovered using two‐phase system extraction. Copyright © 2016 John Wiley & Sons, Ltd.

Phosphorus‐Containing Gradient (Block) Copolymers via RAFT Polymerization and Postpolymerization Modification

Reversible addition‐fragmentation chain transfer (RAFT) copolymerization of styrene (St) and 4‐(diphenylphosphino)styrene (DPPS) is explored to establish the statistical distribution of the phosphine‐functional monomer within the copolymer. RAFT copolymerization of St and DPPS at a variety of feed ratios provides phosphine‐functional copolymers of low dispersity at moderate monomer conversion (Ð < 1.2 at conv. >60%). In all cases, the fraction of DPPS in the resulting polymers is greater than that in the monomer feed. Estimation of copolymerization reactivity ratios indicates DPPS has a strong tendency to homopolymerize while St preferentially copolymerizes with DPPS (rDPPS = 4.4; rSt = 0.31). The utility of the copolymers as macro‐RAFT agents in block copolymer synthesis is demonstrated via chain extension with hydrophilic acrylamide (N,N‐dimethylacrylamide (DMAm)) and acrylate (poly(ethylene glycol) methyl ether acrylate (mPEGA), and di(ethylene glycol) ethyl ether acrylate (EDEGA)) monomers. Finally, access to polymers containing phosphine oxide and phosphonium salt functionalities is shown through postpolymerization modification of the phosphine‐containing copolymers. image

Mechanochemical Synthesis of TiO₂ Nanocomposites as Photocatalysts for Benzyl Alcohol Photo-Oxidation.

TiO2 (anatase phase) has excellent photocatalytic performance and different methods have been reported to overcome its main limitation of high band gap energy. In this work, TiO2-magnetically-separable nanocomposites (MAGSNC) photocatalysts with different TiO2 loading were synthesized using a simple one-pot mechanochemical method. Photocatalysts were characterized by a number of techniques and their photocatalytic activity was tested in the selective oxidation of benzyl alcohol to benzaldehyde. Extension of light absorption into the visible region was achieved upon titania incorporation. Results indicated that the photocatalytic activity increased with TiO2 loading on the catalysts, with moderate conversion (20%) at high benzaldehyde selectivity (84%) achieved for 5% TiO2-MAGSNC. These findings pointed out a potential strategy for the valorization of lignocellulosic-based biomass under visible light irradiation using designer photocatalytic nanomaterials.

An asymmetric small molecule based on thieno[2,3-f]benzofuran for efficient organic solar cells

A new asymmetric small molecule, named R3T-TBFO, with 4,8-bis(2-ethylhexyloxy)-substituted thieno[2,3-f]benzofuran (TBF) as central donor block, has been synthesized and used as donor material in organic solar cells (OSCs). With thermal annealing (TA) and solvent vapor annealing (SVA) treatment, the blend of R3T-TBFO/PC71BM shows a higher hole mobility of 1.37 × 10−4 cm2 V−1 s−1 and a more balanced charge mobilities. Using a structure of ITO/PEDOT:PSS/R3T-TBFO:PC71BM/ZrAcac/Al, the device with TA treatment delivered a moderate power conversion efficiency (PCE) of 5.63%, while device after TA + SVA treatment showed a preferable PCE of 6.32% with a high fill factor (FF) of 0.72.

Chemical Reactivity Window Determines Prodrug Efficiency toward Glutathione Transferase Overexpressing Cancer Cells

Glutathione transferases (GSTs) are often overexpressed in tumors and frequently correlated to bad prognosis and resistance against a number of different anticancer drugs. To selectively target these cells and to overcome this resistance we previously have developed prodrugs that are derivatives of existing anticancer drugs (e.g., doxorubicin) incorporating a sulfonamide moiety. When cleaved by GSTs, the prodrug releases the cytostatic moiety predominantly in GST overexpressing cells, thus sparing normal cells with moderate enzyme levels. By modifying the sulfonamide it is possible to control the rate of drug release and specifically target different GSTs. Here we show that the newly synthesized compounds, 4-acetyl-2-nitro-benzenesulfonyl etoposide (ANS-etoposide) and 4-acetyl-2-nitro-benzenesulfonyl doxorubicin (ANS-DOX), function as prodrugs for GSTA1 and MGST1 overexpressing cell lines. ANS-DOX, in particular, showed a desirable cytotoxic profile by inducing toxicity and DNA damage in a GST-dependent manner compared to control cells. Its moderate conversion of 500 nmol/min/mg, as catalyzed by GSTA1, seems hereby essential since the more reactive 2,4-dinitrobenzenesulfonyl doxorubicin (DNS-DOX) (14000 nmol/min/mg) did not display a preference for GSTA1 overexpressing cells. DNS-DOX, however, effectively killed GSTP1 (20 nmol/min/mg) and MGST1 (450 nmol/min/mg) overexpressing cells as did the less reactive 4-mononitrobenzenesulfonyl doxorubicin (MNS-DOX) in a MGST1-dependent manner (1.5 nmol/min/mg) as shown previously. Furthermore, we show that the mechanism of these prodrugs involves a reduction in GSH levels as well as inhibition of the redox regulatory enzyme thioredoxin reductase 1 (TrxR1) by virtue of their electrophilic sulfonamide moiety. TrxR1 is upregulated in many tumors and associated with resistance to chemotherapy and poor patient prognosis. Additionally, the prodrugs potentially acted as a general shuttle system for DOX, by overcoming resistance mechanisms in cells. Here we propose that GST-dependent prodrugs require a conversion rate "window" in order to selectively target GST overexpressing cells, while limiting their effects on normal cells. Prodrugs are furthermore a suitable system to specifically target GSTs and to overcome various drug resistance mechanisms that apply to the parental drug.

Development of mesoporous ZSM-12 zeolite and its application in alkylation of 2-methylnaphthalene

Desilicated MTW zeolite was evaluated in methylation of 2-methylnaphthalene (2-MN) in a fixed-bed flow reactor at 450 °C. Mesoporous MTW was fabricated via a microwave-assisted desilication process using a harsh alkaline solution to improve the pore volume and the surface area. H-ZSM-12 zeolite was treated with 0.3 M of NaOH solution with different treatment times. Due to the harsh alkaline treatment, micropores were blocked by the deposition of the removed atoms. Due to the importance of methylnaphthalenes intermediates, modified MTW zeolites were evaluated in methylation of 2-MN. Methanol (MeOH), 2-MN and 1,3,5-trimethylbenzene (TMB) were fed to the reactor with a molar ratio of 15:15:70. Higher selectivity to 1-methylnaphthalene (1-MN) was observed rather than dimethylnaphthalene and trimethylnaphthalene with a yield of 13.6, 8 and 2.5 mol%, respectively. Moderate conversion up to 24.1 mol% was reached for 30 min reaction.

Pd(II) complexes of N(4)‐substituted phenylaminoacetohydrazone and biacetylmonooxime: synthesis, characterization, structures and catalytic behaviour towards Suzuki–Miyaura coupling reactions

The reaction of [PdCl2(CH3CN)2] and N(4)‐substituted phenylaminoacetohydrazone ligands (LH) in methanol at room temperature afforded air‐ and moisture‐stable palladium(II) complexes of two types with general formulae [Pd(LH)Cl] and [Pd2(LH)(L)]Cl. An unusual coordination mode of ligand LH is observed, in which the ligand coordinates through N(4)H nitrogen and without enolization of the carbonyl group of the hydrazone moiety in both mono‐ and bimetallic complexes. The crystal structure of the complexes reveals that the oxime LH reacts with [PdCl2(CH3CN)2] presumably via the elimination of HCl from hydrazine NH. All the synthesized Pd(II) complexes were evaluated as catalysts in the Suzuki cross‐coupling reaction of aryl halides, activated 4‐bromoacetophenone and non‐activated bromobenzene, with phenylboronic acid in aqueous medium. In both cases, i.e. with activated and non‐activated aryl halides, all the complexes show moderate conversion leading to biaryls with yields in the range 50–65%. Copyright © 2016 John Wiley & Sons, Ltd.

Efficient Voltage Regulation for Microprocessor Cores Stacked in Vertical Voltage Domains

Due to exponential (Moores law) scaling of advanced CMOS technologies, the challenges associated with delivering power to performance and mobile computing systems are outpacing the capabilities of conventional voltage regulator (VR) topologies. To continue to scale throughput at constant power density, the level of parallelism in microprocessor architectures is expected to increase substantially. In this paper, we present a power conversion topology to provide independent multicore regulation in the 0.8–1.4 V range from a 12-V dc bus. The topology uses a multistage ladder converter to manage power delivery to digital circuits stacked in vertical voltage domains. This approach has several advantages with regard to systems efficiency as it allows a more moderate conversion ratio of the main dc–dc converter. Moreover, the parallel converter only needs to process a fraction of the power of each core as the current can be “recycled” by adjacent cores in the stack. We develop a dynamical model for a multiple-input, multiple-output control scheme that uses a simple integral-control law, augmented with fast voltage- and current-mode feedforward. Measurement results of a discrete prototype verify the control scheme and demonstrate the potential advantages in system efficiency but also emphasize the remaining challenges in meeting stringent VR dynamic response requirements.

Synthesis, characterization, X-ray crystallography analysis, and catalytic activity of bis(2-pyridylmethyl)amine copper complexes containing coupled pendent olefinic arms in atom transfer radical addition (ATRA) reactions

The synthesis, characterization, and catalytic activity of bis(2-pyridylmethyl)amine (BPMA) copper complexes incorporating olefinic pendent arms are reported. Four copper(I) and four copper(II) complexes were synthesized employing four different counterions [chloride (Cl−), perchlorate (ClO4−), trifluoromethanesulfonate (CF3SO3−), and tetraphenylborate (BPh4−)]. The counterions used ranged from coordinating (Cl−) to non-coordinating (BPh4−), producing different coordination modes in respective complexes. Solid state results obtained for the copper(I) complex incorporating the non-coordinating (BPh4−) counterion displayed an associative bond between the metal center and the CC group in the olefinic arm of a neighboring complex. This interaction led to augmentation of the CC bond due to back-bonding from the metal center. Five solid state structures were obtained for the copper(II) complexes with two also displaying intermolecular associative bonding between olefinic pendent arms and the metal center. X-ray crystallography studies showed that the olefinic arm motifs incorporated were hemilabile. Solution studies indicated that the copper complexes had some inherent reducing power and could be potential candidates for use as catalysts in atom transfer radical processes. However, only moderate conversions and yields were obtained in atom transfer radical addition (ATRA) reaction studies performed utilizing the copper complexes due to the presence of a competing reaction.

Donor–acceptor copolymers based on dithienopyrrolobenzothiadiazole: Synthesis, characterization, and photovoltaic applications

In this work, we have developed a nitrogen-bridged pentacyclic dithienopyrrolobenzothiadiazole (TPBT) arene where the two outer electron-rich thiophene moieties are covalently fastened with the central electron-deficient benzothiadiazole core by two nitrogen bridges. The rigid and coplanar TPBT was first copolymerized with alkylthienyl-substituted benzodithiophene (BDT) unit to obtain a new donor–acceptor (D–A) copolymer (PBDT-T) via Stille coupling polymerization. Then, to tune optoelectronic properties of PBDT-T, two random ternary D–A copolymers (PBDT-D30-T70 and PBDT-D70-T30) were synthesized from an electron-rich BDT unit and two electron-deficient units of diketopyrrolopyrrole (DPP) and TPBT that have complementary light absorption behavior. The optical and electrochemical properties of these random terpolymers can be easily tailored by varying the feed ratio of DPP and TPBT. An increase in TPBT induced increased absorption between 300 and 600nm, while higher DPP contents resulted in stronger absorption between 600 and 800nm. Bulk-heterojunction polymer solar cells (PSCs) based on the binary D–A copolymer PBDT-T exhibited a moderate power conversion efficiency (PCE) of 1.86% with a low short-circuit current density (Jsc) of 5.92mAcm−2 and fill factor (FF) of 0.42 due to the narrower absorption band and lower hole mobility, whereas the ternary D–A copolymers displayed improved PCEs benefitting from the increased Jsc. Most importantly, the PSCs based on PBDT-D70-T30 achieved a promising PCE of 4.31% with the highest Jsc of 11.91mAcm−2, indicating that complementary light-absorption random polymer structures have great potential for increasing the photocurrent in bulk heterojunction PSCs.

Ferrites as redox catalysts for chemical looping processes

Spinel ferrites can accommodate oxygen vacancies in their structure and reversibly exchange oxygen with the environment at high temperatures, depending on the partial pressure of oxygen. Therefore their use in Chemical Looping Combustion (CLC) is being studied intensively. In the present work the use of ferrites with the general formula of MeFe2O4 (Me=Mn, Ni, Zn, Co, Cu) as oxygen carriers or potentially reactive supports for oxygen carriers in Chemical Looping Combustion is explored. Polycrystalline ferrite samples are prepared using the conventional ceramic technology of “solid-state reaction”. The performance of the prepared materials is evaluated at a fixed-bed laboratory scale pulse reaction unit. During the fuel oxidation step, methane pulses are injected over the ferrite powder while subsequent oxidation of the solid is performed with gaseous oxygen. The performance of the candidate materials is ranked by comparing the amount of oxygen per mole solid (δ) that can be delivered reversibly to the fuel which corresponds to the Oxygen Transfer Capacity of the different ferrite materials as well as the methane conversion during the fuel oxidation step and the gaseous product distribution. The stability of the materials during multiple reduction–oxidation cycles is evaluated during 5–10 subsequent cycles, each of which is comprised of an activation–regeneration and a solid oxidation step. All the examined ferrites have the ability to deliver their lattice oxygen to a fuel and to some extend regain it in the presence of air. Cu ferrites are very active in CH4 oxidation with maximum conversion higher than 95%, while Zn and Ni ferrites are also highly ranked with methane conversion reaching up to 90% and 78% respectively, however they deactivate very fast after redox cycles. Mn ferrites present relatively low activity (∼30%), while Co ferrites present moderate methane conversion, approximately 68% but remarkable stability during subsequent redox cycles. Cu-, Co- and Ni-ferrites can deliver higher amounts of lattice O, compared to Mn ferrite. The structural and morphological stability of the materials after the multiple redox cycles is examined by X-ray diffraction and SEM–EDS analysis.