Difference In Catalytic Properties Research Articles

Revealing the catalytic kinetics and dynamics of individual Pt atoms at the single-molecule level

SignificanceHere, with single-molecule fluorescence microscopy, we study the catalytic behavior of individual Pt atoms at single-turnover resolution, and then reveal the unique catalytic properties of Pt single-atom catalyst and the difference in catalytic properties between individual Pt atoms and Pt nanoparticles. Further density functional theory calculation indicates that unique catalytic properties of Pt single-atom catalyst could be attributed intrinsically to the unique surface properties of Pt1-based active sites.

Magneli-Phase Titanium Suboxide Nanocrystals as Highly Active Catalysts for Selective Acetalization of Furfural.

Alongside TiO2, Magneli-phase titanium suboxide having the composition of TinO2n-1 is a kind of attractive functional materials composed of titanium. However, there still remain problems to be overcome in the synthesis of titanium suboxide; the existing synthesis methods require high temperature typically over 1000 °C and/or postsynthesis purification. This study presents a novel approach to synthesis of titanium suboxide nanoparticles through solid-phase reaction of TiO2 with TiH2. Crystal phases of titanium suboxide were easily controlled by changing TiO2/TiH2 molar ratios in a TiO2-TiH2 mixed precursor, and a series of titanium suboxide nanoparticles including Ti2O3, Ti3O5, Ti4O7, and Ti8O15 were successfully obtained. The reaction of TiO2 with TiH2 proceeded at a relatively low temperature due to the high reactivity of TiH2, giving titanium suboxide nanoparticles without any postsynthesis purification. Ti2O3 nanoparticles and TiO2 were applied as solid acid catalysts for reaction of furfural with 2-propanol. Ti2O3 showed a high catalytic activity and high selectivity for acetalization of furfural, while TiO2 showed only poor activity for transfer hydrogenation of furfural. The difference in catalytic properties is discussed in terms of the acid properties of Ti2O3 and TiO2.

Crystal Structure-dependent Thermal Stability and Catalytic Performance of AuRu3 Solid-solution Alloy Nanoparticles

Abstract We describe the first investigation into the influence of the crystal structure of AuRu3 alloy nanoparticles (NPs) on their thermal stability and catalytic properties. The hexagonal close-packed (hcp)-AuRu3 alloy NPs show better thermal stability than the face-centered cubic (fcc)-AuRu3 alloy NPs. The difference in catalytic properties was investigated through the oxygen evolution reaction. Both fcc- and hcp-AuRu3 alloy NPs show onset potentials comparable to Ru NPs. However, the hcp alloy NPs show higher durability than the fcc alloy NPs.

Pore size-controlled synthesis of molecular sieves and theirs difference in catalytic properties for Fischer–Tropsch synthesis

Three molecular sieves with different pore size distributions, i.e., mesopore (Al-MCM-41), micropore (ZSM-5) and hierarchical pore (HPMS), were synthesized under hydrothermal condition and characterized by N2 adsorption–desorption. Three cobalt-loaded catalysts, i.e., Co/Al-MCM-41, Co/ZSM-5 and Co/HPMS, were prepared by impregnating cobalt nitrate onto three molecular sieves, respectively, and characterized by X-ray diffraction, scanning electron microscopy, and H2 temperature-programmed reduction (H2-TPR). The H2-TPR results show that the reduction temperature of Co/HPMS is lower than those of Co/Al-MCM-41 and Co/ZSM-5, indicating that Co/HPMS has a better catalytic activity. The selectivity of three catalysts for Fischer–Tropsch synthesis was evaluated in a fixed-bed reactor, and the results show that the pore structure is of important influence on the product distribution. Co/HPMS exhibits significantly good selectivity of C5–11 and C12–18 hydrocarbons (up to 25.6 and 27.7 %, respectively), much higher than those of Co/Al-MCM-41 and Co/ZSM-5, due to the confinement effect of micropore and good diffusibility for long-chain hydrocarbons of mesopore in Co/HPMS.

Propane ammoxidation catalyst prepared by thermally induced spreading of Sb2O3 on V/Al/O-mixed oxide

Mechanical mixtures of Sb2O3 and V/Al/O mixed oxide have been tested as catalysts in the ammoxidation of propane. The results obtained showed that upon addition of Sb2O3 the propane conversion rate and the selectivity to acrylonitrile were decreased but to a limited extent whereas a strong decrease in selectivity to COx was observed to the advantage of selectivity to propene. Sb2O3 completely reacts with the V/Al/O mixed oxide to form a rutile-type V1−xAlxSbO4 phase that spreads over the mixed oxide. If the structure modifications have to be taken into account to explain the difference in catalytic properties, the characterization of the catalysts allowed proposing that they primarily result from the contamination of the surface of the active V/Al/O mixed oxide by Sb species. If the changes in catalytic properties evidenced in the study appear rather unproductive in terms of yield in acrylonitrile, they can be of interest if a process integrated a recycling of the reaction feeds was designed for an industrial application.

Electrochemical CO2 and CO Reduction on Metal-Functionalized Porphyrin-like Graphene

Porphyrin-like metal-functionalized graphene structures have been investigated as possible catalysts for CO2 and CO reduction to methane or methanol. The late transition metals (Cu, Ag, Au, Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os) and some p (B, Al, Ga) and s (Mg) metals comprised the center of the porphyrin ring. A clear difference in catalytic properties compared to extended metal surfaces was observed owing to a different electronic nature of the active site. The preference to bind hydrogen, however, becomes a major obstacle in the reaction path. A possible solution to this problem is to reduce CO instead of CO2. Volcano plots were constructed on the basis of scaling relations of reaction intermediates, and from these plots the reaction steps with the highest overpotentials were deduced. The Rh–porphyrin-like functionalized graphene was identified as the most active catalyst for producing methanol from CO, featuring an overpotential of 0.22 V. Additionally, we have also examined the hydrogen evolution and oxidation reaction, and in their case, too, Rh–porphyrin turned out to be the best catalyst with an overpotential of 0.15 V.

Effects of theCYP2B6*6Allele on Catalytic Properties and Inhibition of CYP2B6 In Vitro: Implication for the Mechanism of Reduced Efavirenz Metabolism and Other CYP2B6 Substrates In Vivo

The mechanism by which CYP2B6*6 allele alters drug metabolism in vitro and in vivo is not fully understood. To test the hypothesis that altered substrate binding and/or catalytic properties contribute to its functional consequences, efavirenz 8-hydroxylation and bupropion 4-hydroxylation were determined in CYP2B6.1 and CYP2B6.6 proteins expressed without and with cytochrome b5 (Cyt b5) and in human liver microsomes (HLMs) obtained from liver tissues genotyped for the CYP2B6*6 allele. The susceptibility of the variant protein to inhibition was also tested in HLMs. Significantly higher V(max) and K(m) values for 8-hydroxyefavirenz formation and ∼2-fold lower intrinsic clearance (Cl(int)) were noted in expressed CYP2B6.6 protein (-b5) compared with that of CYP2B6.1 protein (-b5); this effect was abolished by Cyt b5. The V(max) and Cl(int) values for 4-hydroxybupropion formation were significantly higher in CYP2B6.6 than in CYP2B6.1 protein, with no difference in K(m), whereas coexpression with Cyt b5 reversed the genetic effect on these kinetic parameters. In HLMs, CYP2B6*6/*6 genotype was associated with markedly lower V(max) (and moderate increase in K(m)) and thus lower Cl(int) values for efavirenz and bupropion metabolism, but no difference in catalytic properties was noted between CYP2B6*1/*1 and CYP2B6*1/*6 genotypes. Inhibition of efavirenz 8-hydroxylation by voriconazole was significantly greater in HLMs with the CYP2B6*6 allele (K(i) = 1.6 ± 0.8 μM) than HLMs with CYP2B6*1/*1 genotype (K(i) = 3.0 ± 1.1 μM). In conclusion, our data suggest the CYP2B6*6 allele influences metabolic activity by altering substrate binding and catalytic activity in a substrate- and Cyt b5-dependent manner. It may also confer susceptibility to inhibition.

Methane Combustion Over Copper Chromites Catalysts Prepared by the Sol–Gel Process

Methane combustion was performed over a series of copper chromites (CuCr2O4) catalysts prepared by the sol–gel process (SG). The results were compared with those obtained over commercial CuCr2O4. The samples were characterised by elemental analysis, thermal analysis, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The as-synthesised CuCr2O4 sample exhibited higher specific surface area (248 m2 g−1) with respect to commercial solids (42 m2 g−1). The surface properties were established using XPS. Simultaneously, an increase in the atomic Cr6+/Cr3+ ratio (0.56 for SG catalyst vs. 0.39 for commercial sample) and a decreasing surface copper concentration (8.3%, for SG specimen vs. 17.6% for commercial catalyst) are observed. XPS study revealed also that Cu2+/(Cu° + Cu+) ratio of copper species remained constant (ca. 5) in both catalysts. Structure transformations of CuCr2O4 under reduction-reoxidation conditions showed that the reduction of copper and/or chromium cations from the CuCr2O4 and from delafossite (CuCrO2) structure (CuCr2O4↔CuCrO2 + Cu + Cr2O3↔Cu + Cr2O3) were different. This has lead to a difference in catalytic properties of the catalysts. Catalytic activity of SG catalysts was superior to that of commercial CuCr2O4 tested under the same conditions. Complex hysteresis behaviour for CuCr2O4 catalysts ramped over a temperature range of 220–850 °C where the stables active phases were obtained only after the first ramp of heating under reactants. No catalysts deactivation was further observed after several cycles of heating and cooling. The stabilisation of catalytic activity was attributed to the formation of mixed crystalline phases containing both copper and chromium species.

Analysis of 17β-hydroxysteroid dehydrogenase types 5, 7, and 12 genetic sequence variants in breast cancer cases from French Canadian Families with high risk of breast and ovarian cancer

A family history and estrogen exposure are well-known risk factors for breast cancer. Members of the 17β-hydroxysteroid dehydrogenase family are responsible for important steps in the metabolism of androgens and estrogens in peripheral tissues, including the mammary gland. The crucial biological function of 17β-HSDs renders these genes good candidates for being involved in breast cancer etiology. This study screened for mutations in HSD17B7 and HSD17B12 genes, which encode enzymes involved in estradiol biosynthesis and in AKR1C3, which codes for 17β-HSD type 5 enzyme involved in androgen and progesterone metabolism, to assess whether high penetrance allelic variants in these genes could be involved in breast cancer susceptibility. Mutation screening of 50 breast cancer cases from non- BRCA1/2 high-risk French Canadian families failed to identify germline likely high-risk mutations in HSD17B7, HSD17B12 and AKR1C3 genes. However, 107 sequence variants were identified, including seven missense variants. Assessment of the impact of missense variants on enzymatic activity of the corresponding enzymes revealed no difference in catalytic properties between variants of 17β-HSD types 7 and 12 and wild-type enzymes, while variants p.Glu77Gly and p.Lys183Arg in 17β-HSD type 5 showed a slightly decreased activity. Finally, a haplotype-based approach was used to determine tagging SNPs providing valuable information for studies investigating associations of common variants in these genes with breast cancer risk.

The Roles of Individual Domains of RNase R in Substrate Binding and Exoribonuclease Activity: THE NUCLEASE DOMAIN IS SUFFICIENT FOR DIGESTION OF STRUCTURED RNA

RNase R and RNase II are the two representatives from the RNR family of processive, 3' to 5' exoribonucleases in Escherichia coli. Although RNase II is specific for single-stranded RNA, RNase R readily degrades through structured RNA. Furthermore, RNase R appears to be the only known 3' to 5' exoribonuclease that is able to degrade through double-stranded RNA without the aid of a helicase activity. Consequently, its functional domains and mechanism of action are of great interest. Using a series of truncated RNase R proteins we show that the cold-shock and S1 domains contribute to substrate binding. The cold-shock domains appear to play a role in substrate recruitment, whereas the S1 domain is most likely required to position substrates for efficient catalysis. Most importantly, the nuclease domain alone, devoid of the cold-shock and S1 domains, is sufficient for RNase R to bind and degrade structured RNAs. Moreover, this is a unique property of the nuclease domain of RNase R because this domain in RNase II stalls as it approaches a duplex. We also show that the nuclease domain of RNase R binds RNA more tightly than the nuclease domain of RNase II. This tighter binding may help to explain the difference in catalytic properties between RNase R and RNase II.

An experimental study on Fischer-Tropsch catalysis: Implications for impact phenomena and nebular chemistry

Abstract— Fischer-Tropsch catalysis, by which CO and H2 are converted to CH4 on the surface of transition metals, has been considered to be one of the most important chemical reactions in many planetary processes, such as the formation of the solar and circumplanetary nebulae, the expansion of vapor clouds induced by cometary impacts, and the atmospheric re-entry of vapor condensate due to asteroidal impacts. However, few quantitative experimental studies have been conducted for the catalytic reaction under conditions relevant to these planetary processes. In this study, we conduct Fischer-Tropsch catalytic experiments at low pressures (1.3 times 10−4 bar ≤ P ≤ 5.3 times 10−1 bar) over a wide range of H2/CO ratios (0.25–1000) using pure iron, pure nickel, and iron-nickel alloys. We analyze what gas species are produced and measure the CH4 formation rate. Our results indicate that the CH4 formation rate for iron catalysts strongly depends on both pressure and the H2/CO ratio, and that nickel is a more efficient catalyst at lower pressures and lower H2/CO ratios. This difference in catalytic properties between iron and nickel may come from the reaction steps concerning disproportionation of CO, hydrogenation of surface carbon, and the poisoning of the catalyst. These results suggest that nickel is important in the atmospheric re-entry of impact condensate, while iron is efficient in circumplanetary subnebulae. Our results also indicate that previous numerical models of iron catalysis based on experimental data at 1 bar considerably overestimate CH4 formation efficiency at lower pressures, such as the solar nebula and the atmospheric re-entry of impact condensate.

A novel Ni-CERMET electrode based on a proton conducting electrolyte

Based on the one-chamber fuel cell design by Iwahara a catalytic methane sensor has been developed. The working principle of this sensor is based on the difference in catalytic properties of two electrodes for the CO2 reforming reaction of methane. The sensor is based on a high-temperature proton conducting electrolyte, i.e. SrCe0.95Yb0.05O3−α or CaZr0.9In0.1O3−α. At 500 °C a linear sensor response on the methane partial pressure has been found for a Ru/SrCe0.95Yb0.05O3−α/Pt cell. This cell, however, shows poor long-term stability. The long-term stability of the Ru/SrCe0.95Yb0.05O3−α/Pt cell is improved using a more stable electrolyte material, i.e. CaZr0.9In0.1O3−α(CZI10). Further improvement of the long-term stability of the sensor is achieved using a nickel-CaZr0.9In0.1O3−α CERMET (Ni-CZI10) electrode. The sensor response of a Ni-CZI10/CaZr0.9In0.1O3−α/Pt cell is found to be linear at 600 °C and 700 °C, respectively. The temperature dependence of both the Ru/SrCe0.95Yb0.05O3−α/Pt and the Ni-CZI10/CaZr0.9In0.1O3−α/Pt cell can be explained by the temperature dependence of the catalytic activity of the electrode materials used. This confirms that the obtained EMF is established by a catalytic activity difference between both electrodes. The power output of a Ni-CZI10/CaZr0.9In0.1O3−α/Pt cell is also determined. A combined sensor-fuel cell would have the advantage that it is able to detect the fuel concentration in the gas and, therefore, correct in-situ for fluctuations in the fuel concentration. The power output of the Ni-CZI10/CaZr0.9In0.1O3−α/Pt cell, however, is found to be 0.01 mW · cm−2. This low power output, with respect to values reported in literature for the one-chamber fuel cell, can be explained by the relatively thick electrolyte used, the electrode materials chosen, and the use of the reforming reaction of methane instead of the partial oxidation of methane. However, the feasibility of the combined sensor-fuel cell has been demonstrated.

CoMo/Al2O3 VERSUS NiMo/Al2O3 SULPHIDE CATALYSTS : SENSITIVITY TO REACTION CONDITIONS FOR HDS AND HYDROGENATION

AbstractTwo industrial hydrotreating catalysts, CoMo/Al2O3 and NiMo/Al2O3, were compared with respect to their activity and selectivity In thiophene hydrodesulphurisation and cyclohexene hydrogenation at 280°C and 4 MPa. Their difference in catalytic properties for HDS and hydrogenation was found strongly dependent on the experimental conditions. Addition of small amounts of H2S to the feed inhibits the activity of both catalysts; but at high H2S levels, the catalysts remain active. A new type of site is proposed to operate at high H2S levels. The NiMo catalyst was found far more active than the CoMo catalyst at low H2S pressure, while the two catalysts became equivalent at high H2S levels.

Structural studies on neonatal rat liver glycogen synthase: A comparison between adult and newborn synthase phosphopeptides

Liver glycogen synthase has been isolated from newborn rats and phosphorylated in vitro with the catalytic subunit of cAMP-dependent protein kinase. The isolated newborn synthase b is dependent upon Glc 6-P for activity, like adult synthase b, but has a high affinity toward Glc 6-P, unlike adult synthase b but like adult synthase a. Phosphorylation decreases the newborn synthase affinity toward Glc 6-P to the same value as adult synthase b. A comparison of adult and newborn synthase 32 P i-labeled trypsin and chymotrypsin peptide fragments by sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows that the newborn synthase has structural properties significantly different from the adult enzyme. Thus, a fetal isozyme of synthase in the newborn rat could account, in part, for the difference in catalytic properties, relative to adult synthase.

Modelling active site response towards changes in the protein-core of serine proteases. Aa CNDO/2—INDO SCRF study of subtilisin and thiosubtilisin

The sensitivity of the active site of subtilisin and thiosubtilisin towards surrounding changes mimicked by screening the protein electrostatic field, the charge state of the acid and basic side chains and/or amino terminal group within the selfconsistent reaction field framework is explored numerically. First, a comparative study of the catalytic triads of subtilisin and thiosubtilisin is carried out. A CNDO/2—SCRF scheme is used to calculate energy gaps between the protonated states and by varying the parameters that simulate surrounding changes, the gap's sensitivity is examined. Notable differences appear in the behaviour of these triads which provide a rationale for understanding their difference in catalytic properties. The second test problem is the study of a docking of methylacetate in subtilisin. The active site is completed with the dyad formed by Ser-221 and His-64. The role of Asp-32 is represented via a variable negative charge. A planar and a tetrahedral model substrate have been studied. A significant barrier due to proton reorganization in the dyad has been found in the study of the pathway leading to the formation of a tetrahedral intermediate. The protein favours the tetrahedral conformation of the substrate by lowering this energy barrier. The calculations have been carried out with an INDO—SCRF procedure and a simple docking program. The overall results display interesting trends which are in fairly good agreement with experimental experience. Where other theoretical calculations exist the present work is in agreement with these and provides a supplementary view. The advantage and interest of the present type of simulations reside in the possibility of studying how a system evolves under changes produced in the environments.

Modelling active site response towards changes in the protein-core of serine proteases. A CNDO/2—INDO SCRF study of subtilisin and thiosubtilisin

The sensitivity of the active site of subtilisin and thiosubtilisin towards surrounding changes mimicked by screening the protein electrostatic field, the charge state of the acid and basic side chains and/or amino terminal group within the selfconsistent reaction field framework is explored numerically. First, a comparative study of the catalytic triads of subtilisin and thiosubtilisin is carried out. A CNDO/2—SCRF scheme is used to calculate energy gaps between the protonated states and by varying the parameters that simulate surrounding changes, the gap's sensitivity is examined. Notable differences appear in the behaviour of these triads which provide a rationale for understanding their difference in catalytic properties. The second test problem is the study of a docking of methylacetate in subtilisin. The active site is completed with the dyad formed by Ser-221 and His-64. The role of Asp-32 is represented via a variable negative charge. A planar and a tetrahedral model substrate have been studied. A significant barrier due to proton reorganization in the dyad has been found in the study of the pathway leading to the formation of a tetrahedral intermediate. The protein favours the tetrahedral conformation of the substrate by lowering this energy barrier. The calculations have been carried out with an INDO—SCRF procedure and a simple docking program. The overall results display interesting trends which are in fairly good agreement with experimental experience. Where other theoretical calculations exist the present work is in agreement with these and provides a supplementary view. The advantage and interest of the present type of simulations reside in the possibility of studying how a system evolves under changes produced in the environments.

Drosophila lactate dehydrogenase: developmental aspects.

Partially purified lactate dehydrogenase (LDH) from third-instar larvae displays two bands (one major and one minor) on polyacrylamide gels. Analogous preparations from pupae and adults exhibit three LDH-staining bands (one major and two minor) in a similar pattern. The migration of the major band is similar for larvae, pupae, and adults, while the two minor LDH bands of pupae and adults migrate more slowly than the minor larval band. It has been shown that larval LDH incubated with beta-nicotinamide adenine dinucleotide exhibits two additional minor bands with an electrophoretic mobility similar to that of the minor bands of both pupae and adults. The intensity of the minor larval LDH band (exhibited also by untreated preparations) is drastically reduced. This fact indicates that the life-cycle stage-dependent LDH isozymic distribution is possibly due to a posttranslational effect(s). Highly purified LDH from larvae, pupae, or adults, obtained by an affinity chromatography procedure, displays just one dispersed band, located in the area between the band 5 and the band 6 exhibited by crude extract preparations. These data, in combination with the lack of difference in catalytic properties among enzymes from larvae, pupae, and adults, suggest that LDH synthesis is controlled by the same single structural gene at all developmental stages.

Isolation of proteins with carbonyl reductase activity and prostaglandin-9-ketoreductase activity from chicken kidney.

Kidney has the greatest capacity among the tissues of chicken for reducing aromatic ketones, and two ketone reductases were separated from this tissue by DEAE-cellulose chromatography and isolated. Though both are monomeric proteins with a molecular weight of 29,500, and with similar amino acid compositions and immunological properties, they differ in their pI values. The two enzyme species show no apparent difference in catalytic properties; aromatic ketones, aldehydes and quinones are reduced at high rates and alicyclic ketones such as 3-ketosteroids and prostaglandin E2 at low rates. The substrate affinity for several representative substrates at pH 7.2 is higher than that at the optimal pH of 6.3. Both enzymes prefer NADPH to NADH as a cofactor. Low NADP+-dependent reverse reactions occur with 9- and 15-hydroxyprostaglandins and certain alcohols as substrates. The enzymes show similar sensitivities to heavy metal ions, SH-reagents, quercitrin, indomethacin, and FMN.