Substituting Chromium in Iron-Based Catalysts for the High-Temperature Water-Gas Shift Reaction.

A set of doped iron oxides (chromium, aluminum, gallium, indium, manganese, zinc, niobium) were prepared by a one-step coprecipitation/calcination approach evaluated for their WGS activity under industrially relevant conditions and characterized in detail. The WGS activity after ageing the doped catalyst for 4 days at 25 bar follows the order chromium ≈ aluminum > gallium > indium > manganese > zinc > niobium for copper-codoped catalysts. The activated catalysts predominantly consist of magnetite, irrespective of the dopant. Mössbauer spectra of aged catalysts showed that aluminum and zinc occupy both tetrahedral and octahedral sites of magnetite, while chromium, gallium, indium, manganese, and niobium preferentially substitute octahedral iron. The incorporation of trivalent metal ions of similar size to octahedral Fe3+ (i.e., chromium, aluminum, gallium) results in moderate to high CO conversion, irrespective of incorporation in tetrahedral or octahedral sites. The substitution of Fe2+ with Mn2+ results in an increased Fe3+/Fe2+ ratio. Incorporation of Zn2+ in tetrahedral sites (replacing Fe3+ ions) leads to a complex structure where the charge balance is compensated from the octahedral sites. Separate dopant metal oxide phases were observed in indium- and niobium-doped catalysts. XPS shows that copper is present as a separate phase in activated copper-codoped catalysts. Aluminum is identified as the most promising promoter for substituting chromium in commercial high-temperature WGS catalysts on the basis of their similar high CO conversion although incorporation of these dopants into the magnetite structure differed substantially.

Reactor for nano-focused x-ray diffraction and imaging under catalytic in situ conditions.

A reactor cell for in situ studies of individual catalyst nanoparticles or surfaces by nano-focused (coherent) x-ray diffraction has been developed. Catalytic reactions can be studied in flow mode in a pressure range of 10-2-103 mbar and temperatures up to 900 °C. This instrument bridges the pressure and materials gap at the same time within one experimental setup. It allows us to probe in situ the structure (e.g., shape, size, strain, faceting, composition, and defects) of individual nanoparticles using a nano-focused x-ray beam. Here, the setup was used to observe strain and facet evolution of individual model Pt catalysts during in situ experiments. It can be used for heating other (non-catalytically active) nanoparticles (e.g., nanowires) in inert or reactive gas atmospheres or vacuum as well.

Mechanism and microkinetics of the Fischer-Tropsch reaction.

The increasing availability of quantum-chemical data on surface reaction intermediates invites one to revisit unresolved mechanistic issues in heterogeneous catalysis. One such issue of particular current interest is the molecular basis of the Fischer-Tropsch reaction. Here we review current molecular understanding of this reaction that converts synthesis gas into longer hydrocarbons where we especially elucidate recent progress due to the contributions of computational catalysis. This perspective highlights the theoretical approach to heterogeneous catalysis that aims for kinetic prediction from quantum-chemical first principle data. Discussion of the Fischer-Tropsch reaction from this point of view is interesting because of the several mechanistic options available for this reaction. There are many proposals on the nature of the monomeric single C atom containing intermediate that is inserted into the growing hydrocarbon chain as well as on the nature of the growing hydrocarbon chain itself. Two dominant conflicting mechanistic proposals of the Fischer-Tropsch reaction that will be especially compared are the carbide mechanism and the CO insertion mechanism, which involve cleavage of the C-O bond of CO before incorporation of a CHx species into the growing hydrocarbon chain (the carbide mechanism) or after incorporation into the growing hydrocarbon chain (the CO insertion mechanism). The choice of a particular mechanism has important kinetic consequences. Since it is based on molecular information it also affects the structure sensitivity of this particular reaction and hence influences the choice of catalyst composition. We will show how quantum-chemical information on the relative stability of relevant reaction intermediates and estimates of the rate constants of corresponding elementary surface reactions provides a firm foundation to the kinetic analysis of such reactions and allows one to discriminate between the different mechanistic options. The paper will be concluded with a short perspective section dealing with the needs for future research. Many of the current key questions on the physical chemistry as well as computational study of heterogeneous catalysis relate to particular topics for further research on the fundamental aspects of Fischer-Tropsch catalysis.

Cyanide leaching of Au/CeO2: highly active gold clusters for 1,3-butadiene hydrogenation.

Ceria-supported gold catalysts before and after leaching by NaCN were investigated by X-ray absorption spectroscopy at the Au L(III) edge. After gold leaching, isolated gold cations remain in close interaction with the support. These ions form an ideal precursor to very small clusters of a few gold atoms upon reduction. The resulting gold clusters exhibit a very high intrinsic activity in the hydrogenation of 1,3-butadiene, which is at least one order of magnitude higher than that of the nanometre-sized gold particles in the non-leached parent catalyst. These findings point to a very strong structure sensitivity of the gold-catalyzed hydrogenation of dienes.

ELISPOT and intracellular cytokine staining: novel assays for quantifying T cell responses in the chicken.

The measurement of T cell responses in chickens, not only for quantitative aspects but also for the qualitative nature of the responses, becomes increasingly important. However, there are very few assays available to measure T cell function. Therefore, we have developed enzyme-linked immunosorbent spot assay (ELISPOT) and an intracellular cytokine staining (ICCS) assay. ELISPOT assay for the detection of chicken interferon-gamma (ChIFN-gamma) production was set up and shown to be reproducible for both polyclonal and antigen-specific stimuli such as Newcastle disease virus (NDV). However, the ELISPOT assay lacks the ability to identify individual cytokine-producing cells. Separation of CD4+ and CD8+ T cell populations gave additional information, but appeared to have the disadvantage of a loss of cell interactions during stimulation. In a further refinement, individual cells were identifiable by ICCS, which gives the possibility to characterize for multiple characteristics, such as cytokine production and phenotype of the cell. Using ICCS, ChIFN-gamma production was evaluated. Although cells were detected at only low frequencies, polyclonal stimulation of peripheral blood mononuclear cell (PBMC) or spleen cells resulted in a significant increase in ChIFN-gamma production by CD4+ and CD8+ cells.

On two alternative mechanisms of ethane activation over ZSM-5 zeolite modified by Zn2+ and Ga1+ cations.

The activation of ethane over zinc- and gallium-modified HZSM-5 dehydrogenation catalysts was studied by diffuse reflectance infrared spectroscopy. Hydrocarbon activation on HZSM-5 modified by bivalent Zn and univalent Ga cations proceeds via two distinctly different mechanisms. The stronger molecular adsorption of ethane by the acid-base pairs formed by distantly separated cationic Zn2+ and basic oxygen sites results already at room temperature in strong polarizability of adsorbed ethane and subsequent heterolytic dissociative adsorption at moderate temperatures. In contrast, molecular adsorption of ethane on Ga+ cations is weak. At high temperatures dissociative hydrocarbon adsorption takes place, resulting in the formation of ethyl and hydride fragments coordinating to the cationic gallium species. Whereas in the zinc case a Brønsted acid proton is formed upon ethane dissociation, decomposition of the ethyl fragment on gallium results in gallium dihydride species and does not lead to Brønsted acid protons. This difference in alkane activation has direct consequences for hydrocarbon conversions involving dehydrogenation.

Immunoprecipitation and isoelectric focusing of sheep MHC class I antigens reveal higher complexity than serology.

Biochemical and serological methods were used to characterize sheep MHC class I polymorphism at the product level. The cells of 65 selected animals were subjected to immunoprecipitation and one-dimensional isoelectric focusing (IEF) with two cross-reacting monoclonal antibodies, B1.1G6 and HC-10. We were able to define up to 18 distinct haplotypes in the Latxa breed sample. Most of the locally defined serological specificities were confirmed or subdivided by biochemical typing. As IEF detected antigens not yet defined by serology, it provided us with a guide to producing more specific antisera by appropriate immunizations. Lastly, evidence of expression of two class I loci products was found.

N2O decomposition over Fe/ZSM-5: reversible generation of highly active cationic Fe species.

Fe-oxide species in Fe/ZSM-5 (prepared by chemical vapor deposition of FeCl3)--active in N2O decomposition--react with zeolite protons during high temperature calcination to give highly active cationic Fe species, this transformation being reversible upon exposure to water vapor at lower temperature.

Selection of T-cell epitopes from foot-and-mouth disease virus reflects the binding affinity to different cattle MHC class II molecules.

The major histocompatibility complex (MHC)-restricted selection of T-cell epitopes of foot-and-mouth disease virus (FMDV) by individual cattle MHC class II DR (BoLA-DR) molecules was studied in a direct MHC-peptide binding assay. By in vitro priming of T lymphocytes derived from animals homozygous for both MHC class I and II, five T-cell epitopes were analyzed in the context of three MHC class II haplotypes. We found that the presentation of these T-cell epitopes was mediated by DR molecules, since blocking this pathway of antigen presentation using monoclonal antibody TH14B completely abolished the proliferative responses against the peptides. To study the DR-restricted presentation of these T-cell epitopes, a direct MHC-peptide binding assay on isolated cattle DR molecules was developed. Purified cattle MHC class II DR molecules of the BoLA-DRB3*0201, BoLA-DRB3*1101, and BoLA-DRB3*1201 alleles were isolated from peripheral blood mononuclear cells. For each allele, one of the identified T-cell epitopes was biotinylated, and used as a marker peptide for the development of a competitive MHC-peptide binding assay. Subsequently, the T-cell epitopes of FMDV with functionally defined MHC class II specificity were analyzed in this binding assay. The affinity of the epitopes to bind to certain DR molecules was significantly correlated to the capacity to induce T-cell proliferation. This demonstrated at the molecular level that the selection of individual T-cell epitopes found at the functional level was indeed the result of MHC restriction.

DNA typing for BoLA class I using sequence-specific primers (PCR-SSP).

The analysis of cattle MHC (BoLA) class I gene expression is an essential component of studies on immune responses and susceptibility to disease. International BoLA workshops have generated data and reagents that allow discrimination of class I molecules at the haplotype level, but progress has been limited by difficulties encountered in defining single alleles. Our aim in this study was to develop a DNA-based system for improved identification of expressed class I alleles, utilizing available cDNA sequences derived from cattle carrying a series of serologically defined class I specificities. This method has allowed more accurate typing of animals for expression of the class I genes present within a small number of haplotypes. The method has also reliably differentiated between allelic variants (identified by prior sequence analysis) and has split existing serological specificities. The data show that MHC class I genes in cattle are more polymorphic than demonstrated by serology and biochemical analysis.

The specificity of anti-HLA class II monoclonal antibodies in cattle.

At the Eleventh International HLA Histocompatibility Workshop, numerous anti-HLA class II monoclonal antibodies (mAb) were tested. For several of the polymorphic mAb, one epitope for binding has been mapped within the antigen-binding site of the class II molecules. Screening of the available bovine DRB3 and DQB exon 2 sequences revealed that some of the key amino acid (AA) motifs of these epitopes were present in cattle as well, and the question was raised whether this sharing of key AA motifs might cause interspecies cross-reactivity. Eight polymorphic anti-HLA class II mAb (seven anti-HLA DRB1 and one anti-HLA DQB) were selected for analysis of their reactivity towards bovine lymphocytes. In addition, the monomorphic anti-HLA class II mAb, 7.5.10.1, was selected for analysis, as this mAb was described to detect class II polymorphism in cattle. Flow cytometry and lymphocyte microcytotoxicity testing revealed that five of the polymorphic anti-HLA mAb were reactive with bovine lymphocytes. Furthermore, the anti-bovine reactivity of 7.5.10.1 was confirmed. These findings were supported by biochemical analysis. The anti-bovine reaction of the anti-HLA mAb did not correspond with the expected reaction, which was based on the presence of the AA, postulated to be responsible for recognition. Therefore, we suggest that the patterns of reactivity of the anti-HLA mAb are not always determined by one epitope.

Antibody responses against epitopes on the F protein of bovine respiratory syncytial virus differ in infected or vaccinated cattle.

The fusion protein F of bovine respiratory syncytial virus (BRSV) is an important target for humoral and cellular immune responses, and antibodies against the F protein have been associated with protection. However, the F protein can induce antibodies with different biological activity, possibly related to distinct antigenic regions on the protein. Therefore, epitopes were mapped on the F protein using monoclonal antibodies. Two epitopes (A and B) were identified that induced neutralizing antibodies, and one epitope (C) that did not elicit neutralizing antibodies. Subsequently, antibody responses were analysed against these epitopes in cattle sera after natural infection, experimental infection or vaccination. After natural infection or reinfection, the antibody titres against epitope A were significantly higher than those against epitope B or C. After experimental infection and after vaccination with an inactivated vaccine, antibody titres against epitope B and C were significantly higher than after natural infection. Conversely, virus neutralizing antibody titres were significantly lower in these animals with higher antibody titres against epitopes B and C than in naturally infected cattle. Because after natural infection the epitope-specific-antibody titres against epitope A, B or C differed markedly between the cattle, the magnitude of the antibody titres against epitope A, B or C in relation to the major histocompatibility complex (MHC) genes of cattle (BoLA) was studied. The magnitude of the antibody responses against epitope A of the F protein, but not against the G protein, appeared to be associated with the bovine lymphocyte antigen (BoLA) haplotype.

THE SPECIFICITY OF ANTI-HLA CLASS II MONOCLONAL ANTIBODIES IN CATTLE.

At the Eleventh International HLA Histocompatibility Workshop, numerous anti-HLA class II monoclonal antibodies (mAb) were tested. For several of the polymorphic mAb, one epitope for binding has been mapped within the antigen-binding site of the class II molecules. Screening of the available bovine DRB3 and DQB exon 2 sequences revealed that some of the key amino acid (AA) motifs of these epitopes were present in cattle as well, and the question was raised whether this sharing of key AA motifs might cause interspecies cross-reactivity. Eight polymorphic anti-HLA class II mAb (seven anti-HLA DRB1 and one anti-HLA DQB) were selected for analysis of their reactivity towards bovine lymphocytes. In addition, the monomorphic anti-HLA class II mAb, 7.5.10.1, was selected for analysis, as this mAb was described to detect class II polymorphism in cattle. Flow cytometry and lymphocyte microcytotoxicity testing revealed that five of the polymorphic anti-HLA mAb were reactive with bovine lymphocytes. Furthermore, the anti-bovine reactivity of 7.5.10.1 was confirmed. These findings were supported by biochemical analysis. The anti-bovine reaction of the anti-HLA mAb did not correspond with the expected reaction, which was based on the presence of the AA, postulated to be responsible for recognition. Therefore, we suggest that the patterns of reactivity of the anti-HLA mAb are not always determined by one epitope.

Sequences derived from the highly antigenic VP1 region 140 to 160 of foot-and-mouth disease virus do not prime for a bovine T-cell response against intact virus.

Although VP1 region 140 to 160 of foot-and-mouth disease virus (FMDV) is able to elicit neutralizing antibody in cattle, the protection against virus challenge that is conferred by peptide immunization is often poor. Here, we show that bovine T cells primed with peptides derived from this region generally show no reactivity to intact FMDV. In contrast, T-cell epitope VP4[20-34] is able to prime for a virus-specific response.

Uterine carcinomas in mother cats after intrafetal inoculation of allogeneic tumor cells (K248 C and P).

Three out of 13 queens that had undergone injection of tumor cells from an allogeneic feline mammary carcinoma cell line through the wall of the pregnant uterus developed a carcinoma of the uterus. The possible role of immune tolerance associated with pregnancy and/or major histocompatibility complex (MHC) compatibility is discussed.

The influence of MHC polymorphism on the selection of T-cell determinants of FMDV in cattle.

There is a quest for the development of a new generation of vaccines consisting of well-defined subunit antigens. For a number of practical reasons it is attractive to develop vaccines on the basis of synthetic peptides. However, their efficacy may be limited by genetic restrictions imposed on T-cell recognition via major histocompatibility complex (MHC) polymorphism, as shown by many studies using inbred animal species. To study the effect of MHC polymorphism in an outbred species, we selected four cattle homozygous for different A-DR-DQ haplotypes, and another four cattle which shared one haplotype in combination with a haplotype of one of the MHC homozygous animals. We analysed responses to synthetic peptides comprising defined T-cell epitopes of foot-and-mouth disease virus (FMDV) in this selected group of FMDV-vaccinated cattle. This analysis shows that even in outbred animals. MHC polymorphism influences the responses to synthetic peptides. Interestingly, one of the peptides, VP4[20-34], was recognized in association with at least four different MHC haplotypes. Fine specificity analysis of this peptide revealed subtle shifts in the core epitope recognized. All peptides that induced lymphocyte proliferation in vitro were found to induce a T-helper type-1 (Th1) type of response, irrespective of the MHC haplotype involved. Together, these data support the notion that individuals carrying distinct MHC types can be vaccinated successfully by vaccines that include only a limited number of peptides. In the design of a peptide vaccine against FMDV we suggest inclusion of the highly conserved VP4 sequence 20-34.

T cell-stimulatory fragments of foot-and-mouth disease virus released by mild treatment with cathepsin D.

Cathepsin D and cathepsin B are endosomal/lysosomal proteases that are thought to play a role during in vivo antigen processing, releasing fragments for binding to major histocompatibility complex class II products and subsequent presentation to T cells. Here we treated purified foot-and-mouth disease virus (FMDV) strain A10Holland with both enzymes. Cathepsin D, but not cathepsin B, was shown to release fragments from reduced or non-reduced FMDV under mild conditions in vitro. Twenty-eight predominant cathepsin D-released fragments were purified by HPLC and identified by amino acid composition analysis and sequencing. The unseparated set of fragments produced (the digest) was able to stimulate T cells from eight vaccinated cattle. With respect to the response to intact virus the extent of the response to the digest differed between animals: four animals could be classified as good responders, three as intermediate responders and one as a low responder. Subsequently, we investigated the proliferative T cell response to a large set of synthetic peptides in detail for two animals, one belonging to the group of good responders, the other being the low responder. The peptides covered all 28 cathepsin D-released fragments analysed and also several sequences not recovered from the digest. In this way seven T cell sites could be identified, five of which coincided with cathepsin D-released fragments. The other two T cell sites were VP2[54-72], being a homologue of a T cell site identified for FMDV strain O1K and the N terminus of VP4. Whether the most dominantly recognized T cell site was recovered from the digest or not was shown to be related to the good or low response to the digest. These findings suggest a role for cathepsin D in the release of some but not all T cell-stimulatory fragments from FMDV.

Effect of climatic stress on the immunological reactivity of weaned pigs.

Weaned pigs exposed daily to either unpredictable draught (experiment 1) or intermittent unpredictable draught (experiment 2) showed different lymphocyte blastogenic responses after mitogenic stimulation with phytohaemagglutinin (PHA) and concanavalin A (ConA). In both experiments PHA skin test responses were lower for draught exposed pigs than for control pigs and leucocyte numbers or profiles were altered compared to those of control pigs. Superoxide production and chemiluminescence of porcine granulocytes were similar for draught exposed and control animals. Furthermore, serum globulin content did not differ significantly between pigs in the experimental and control room. The strong increase in serum gamma-globulin after the Aujeszky Disease Virus (ADV)-challenge was the same for draught exposed and control pigs. The same held for the lymphocyte blastogenic response with ADV protein as antigenic stimulus. The present study shows the effects of climatic stress on immunological reactivity, which may reflect a homeostatic disturbance of the pig's immune system elicited by exposure to unpredictable draught.

Biochemical characterization of bovine MHC DQ allelic variants by one-dimensional isoelectric focusing.

Previous studies on expressed bovine MHC class II polymorphism using one-dimensional isoelectric focusing (1D-IEF) allowed the identification of at least 12 allelic variants of the DRB3 gene. So far, only limited data have been available on the expression of other class II genes. The present study involved biochemical analysis of bovine MHC class II molecules using a set of monoclonal antibodies presupposed to be bovine DR and DQ reactive. After essential modification of the standard electrophoresis conditions used for 1D-IEF typing of bovine DR products, biochemical polymorphism was observed for non-DR molecules, revealing polymorphic sets of basic and acidic focusing bands. Because of the extensive DNA polymorphism described for bovine DQA and DQB genes, and the apparent similarity with the focusing pattern of human DQ products, these molecules were considered to be the bovine DQ homologues. The definition of the DQ-associated banding patterns was made possible by using two half-sib sire families. Four different DQA-like patterns and nine DQB-like patterns were detected. Segregation of the DQ types was supported by serological class I and class II typing. These results show that it is now possible to discriminate between expressed bovine DR and DQ polymorphism.