Reduction Property

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Burtron H Davis - One of the best experts on this subject based on the ideXlab platform.

  • fischer tropsch synthesis study of the promotion of pt on the Reduction Property of co al2o3 catalysts by in situ exafs of co k and pt liii edges and xps
    Journal of Synchrotron Radiation, 2004
    Co-Authors: Gary Jacobs, John A Chaney, Patricia M Patterson, Tapan K Das, Julie C Maillot, Burtron H Davis
    Abstract:

    The addition of platinum metal to cobalt/alumina-based Fischer-Tropsch synthesis (FTS) catalysts increases both the Reduction rate and, consequently, the density of active cobalt sites. Platinum also lowers the temperature of the two-step conversion of cobalt oxide to cobalt metal observed in temperature programmed Reduction (TPR) as Co3O4 to CoO and CoO to Co0. The interaction of the alumina support with cobalt oxide ultimately determines the active site density of the catalyst surface. This interaction can be controlled by varying the cobalt loading and dispersion, selecting supports with differing surface areas or pore sizes, or changing the noble metal promoter. However, the active site density is observed to depend primarily on the cluster size and extent of Reduction, and there is a direct relationship between site density and FTS rate. In this work, in situ extended X-ray absorption fine structure (EXAFS) at the LIII edge of Pt was used to show that isolated Pt atoms interact with supported cobalt clusters without forming observable Pt--Pt bonds. K-edge EXAFS was also used to verify that the cobalt cluster size increases slightly for those systems with Pt promotion. X-ray absorption near-edge spectroscopy (XANES) was used to examine the remaining cobalt clusters after the first stage of TPR, and it revealed that the species were almost entirely cobalt (II) oxide. After the second stage of TPR to form cobalt metal, a residual oxide persists in the sample, and this oxide has been identified as cobalt (II) aluminate using X-ray photoelectron spectroscopy (XPS). Sequential in situ Reduction of promoted and unpromoted systems was also monitored through XPS, and Pt was seen to increase the extent of cobalt Reduction by a factor of two.

  • fischer tropsch synthesis study of the promotion of re on the Reduction Property of co al2o3 catalysts by in situ exafs xanes of co k and re liii edges and xps
    Applied Catalysis A-general, 2004
    Co-Authors: Gary Jacobs, John A Chaney, Patricia M Patterson, Tapan K Das, Burtron H Davis
    Abstract:

    A direct relationship between the Fischer–Tropsch synthesis (FTS) rate and the number of surface cobalt atoms available for reaction is usually obtained. For Co/Al2O3 catalysts in particular, the site density depends on two primary factors: (1) the average size of the cobalt clusters on the support; and (2) the fraction of cobalt reduced to the metallic state. The addition of small amounts of noble metal promoters, such as Pt and Ru to cobalt alumina, may catalyze the Reduction of cobalt oxide shifting the temperature of Reduction of both steps (Co3O4→CoO and CoO→Co0) to lower temperatures. However, Re affects only the second step. Re is reduced at a higher temperature than Pt or Ru, and at approximately the same temperature as the first step of cobalt Reduction (Co3O4→CoO). Thus, Re metal is present to catalyze only the second step. In situ extended X-ray absorption fine structure (EXAFS) at the LIII edge of Re has been used to show that there is direct contact of Re with cobalt atoms, while evidence for ReRe bonds is not observed. Even though direct atom-to-atom contact is found, temperature-programmed Reduction (TPR) suggests that hydrogen spillover from the promoter to cobalt oxide clusters is important for the catalysis of cobalt oxide Reduction. In situ EXAFS at the K edge of Co shows that the average cobalt cluster size decreases with increasing Re loading. Re promotes Reduction of smaller species which interact with the support, and therefore, for a given Reduction temperature, the average cobalt metal cluster size decreases as a function of increasing Re content. After Reduction at a temperature slightly above the first peak in the TPR (Co3O4→CoO), the species remaining on the surface displayed XANES spectra identical to that of CoO. After Reduction at a temperature above the second broad TPR peak, XPS showed that a residual oxide species was present, with a binding energy equivalent to cobalt aluminate.

Okyay Kaynak - One of the best experts on this subject based on the ideXlab platform.

  • analysis of the noise Reduction Property of type 2 fuzzy logic systems using a novel type 2 membership function
    Systems Man and Cybernetics, 2011
    Co-Authors: Mojtaba Ahmadieh Khanesar, Mohammad Teshnehlab, Erdal Kayacan, Okyay Kaynak
    Abstract:

    In this paper, the noise Reduction Property of type-2 fuzzy logic (FL) systems (FLSs) (T2FLSs) that use a novel type-2 fuzzy membership function is studied. The proposed type-2 membership function has certain values on both ends of the support and the kernel and some uncertain values for the other values of the support. The parameter tuning rules of a T2FLS that uses such a membership function are derived using the gradient descend learning algorithm. There exist a number of papers in the literature that claim that the performance of T2FLSs is better than type-1 FLSs under noisy conditions, and the claim is tried to be justified by simulation studies only for some specific systems. In this paper, a simpler T2FLS is considered with the novel membership function proposed in which the effect of input noise in the rule base is shown numerically in a general way. The proposed type-2 fuzzy neuro structure is tested on different input-output data sets, and it is shown that the T2FLS with the proposed novel membership function has better noise Reduction Property when compared to the type-1 counterparts.

  • a novel type 2 fuzzy membership function application to the prediction of noisy data
    International Conference on Computational Intelligence for Measurement Systems and Applications, 2010
    Co-Authors: Mojtaba Ahmadieh Khanesar, Mohammad Teshnehlab, Erdal Kayacan, Okyay Kaynak
    Abstract:

    A novel, diamond-shaped type-2 fuzzy member- ship function is introduced in this study. The proposed type-2 fuzzy membership function has certain values on 0 and 1, but it has some uncertainties for the other membership values. It has been shown that the type-2 fuzzy system using this type of membership function introduced in this study has some noise Reduction Property in the presence of noisy inputs. The appropriate parameter selection to be able to achieve noise Reduction Property is also considered. A hybrid method consisting of particle swarm optimization (PSO) and gradient descent (GD) algorithm is used to optimize the parameters of the proposed type-2 fuzzy system. PSO is a derivative-free optimizer, and the possibility of the entrapment of this optimizer in local minimums is less than the gradient descent method. The proposed type-2 fuzzy system and the hybrid parameter estimation method are then tested on the prediction of a noisy, chaotic dynamical system. The simulation results show that the type-2 fuzzy predictor with the proposed novel membership functions shows a superior performance when compared to the other existing type-2 fuzzy systems in the presence of noisy inputs.

Erdal Kayacan - One of the best experts on this subject based on the ideXlab platform.

  • type 2 fuzzy logic trajectory tracking control of quadrotor vtol aircraft with elliptic membership functions
    IEEE-ASME Transactions on Mechatronics, 2017
    Co-Authors: Erdal Kayacan, Reinaldo Maslim
    Abstract:

    Emerging applications of quadrotor vertical take-off and landing (VTOL) unmanned aerial vehicles in various fields have created a need for demanding controllers that are able to counter several challenges, inter alia, nonlinearity, underactuated dynamics, lack of modeling, and uncertainties in the working environment. This study compares and contrasts type-1 and type-2 fuzzy neural networks (T2FNNs) for the trajectory tracking problem of quadrotor VTOL aircraft in terms of their tracking accuracy and control efforts. A realistic trajectory consisting of both straight lines and curvatures for a surveillance operation with minimum snap Property, which is feasible regarding input constraints of the quadrotor, is generated to evaluate the proposed controllers. In order to imitate the outdoor noisy and time-varying working conditions, realistic uncertainties, such as wind and gust disturbances, are fed to the real-time experiment in the laboratory environment. Furthermore, a cost function based on the integral of the square of the sliding surface, which gives the optimal parameter update rules, is used to train the consequent part parameters of the T2FNN. Thanks to the learning capability of the proposed controllers, experimental results show the efficiency and efficacy of the learning algorithms that the proposed T2FNN-based controller with the optimal tuning algorithm is 50% superior to a conventional proportional-derivative (PD) controller in terms of control accuracy but requires more control effort. T2FNN structures are also shown to possess better noise Reduction Property as compared to their type-1 counterparts in the presence of unmodeled noise and disturbances.

  • analysis of the noise Reduction Property of type 2 fuzzy logic systems using a novel type 2 membership function
    Systems Man and Cybernetics, 2011
    Co-Authors: Mojtaba Ahmadieh Khanesar, Mohammad Teshnehlab, Erdal Kayacan, Okyay Kaynak
    Abstract:

    In this paper, the noise Reduction Property of type-2 fuzzy logic (FL) systems (FLSs) (T2FLSs) that use a novel type-2 fuzzy membership function is studied. The proposed type-2 membership function has certain values on both ends of the support and the kernel and some uncertain values for the other values of the support. The parameter tuning rules of a T2FLS that uses such a membership function are derived using the gradient descend learning algorithm. There exist a number of papers in the literature that claim that the performance of T2FLSs is better than type-1 FLSs under noisy conditions, and the claim is tried to be justified by simulation studies only for some specific systems. In this paper, a simpler T2FLS is considered with the novel membership function proposed in which the effect of input noise in the rule base is shown numerically in a general way. The proposed type-2 fuzzy neuro structure is tested on different input-output data sets, and it is shown that the T2FLS with the proposed novel membership function has better noise Reduction Property when compared to the type-1 counterparts.

  • a novel type 2 fuzzy membership function application to the prediction of noisy data
    International Conference on Computational Intelligence for Measurement Systems and Applications, 2010
    Co-Authors: Mojtaba Ahmadieh Khanesar, Mohammad Teshnehlab, Erdal Kayacan, Okyay Kaynak
    Abstract:

    A novel, diamond-shaped type-2 fuzzy member- ship function is introduced in this study. The proposed type-2 fuzzy membership function has certain values on 0 and 1, but it has some uncertainties for the other membership values. It has been shown that the type-2 fuzzy system using this type of membership function introduced in this study has some noise Reduction Property in the presence of noisy inputs. The appropriate parameter selection to be able to achieve noise Reduction Property is also considered. A hybrid method consisting of particle swarm optimization (PSO) and gradient descent (GD) algorithm is used to optimize the parameters of the proposed type-2 fuzzy system. PSO is a derivative-free optimizer, and the possibility of the entrapment of this optimizer in local minimums is less than the gradient descent method. The proposed type-2 fuzzy system and the hybrid parameter estimation method are then tested on the prediction of a noisy, chaotic dynamical system. The simulation results show that the type-2 fuzzy predictor with the proposed novel membership functions shows a superior performance when compared to the other existing type-2 fuzzy systems in the presence of noisy inputs.

Gary Jacobs - One of the best experts on this subject based on the ideXlab platform.

  • fischer tropsch synthesis study of the promotion of pt on the Reduction Property of co al2o3 catalysts by in situ exafs of co k and pt liii edges and xps
    Journal of Synchrotron Radiation, 2004
    Co-Authors: Gary Jacobs, John A Chaney, Patricia M Patterson, Tapan K Das, Julie C Maillot, Burtron H Davis
    Abstract:

    The addition of platinum metal to cobalt/alumina-based Fischer-Tropsch synthesis (FTS) catalysts increases both the Reduction rate and, consequently, the density of active cobalt sites. Platinum also lowers the temperature of the two-step conversion of cobalt oxide to cobalt metal observed in temperature programmed Reduction (TPR) as Co3O4 to CoO and CoO to Co0. The interaction of the alumina support with cobalt oxide ultimately determines the active site density of the catalyst surface. This interaction can be controlled by varying the cobalt loading and dispersion, selecting supports with differing surface areas or pore sizes, or changing the noble metal promoter. However, the active site density is observed to depend primarily on the cluster size and extent of Reduction, and there is a direct relationship between site density and FTS rate. In this work, in situ extended X-ray absorption fine structure (EXAFS) at the LIII edge of Pt was used to show that isolated Pt atoms interact with supported cobalt clusters without forming observable Pt--Pt bonds. K-edge EXAFS was also used to verify that the cobalt cluster size increases slightly for those systems with Pt promotion. X-ray absorption near-edge spectroscopy (XANES) was used to examine the remaining cobalt clusters after the first stage of TPR, and it revealed that the species were almost entirely cobalt (II) oxide. After the second stage of TPR to form cobalt metal, a residual oxide persists in the sample, and this oxide has been identified as cobalt (II) aluminate using X-ray photoelectron spectroscopy (XPS). Sequential in situ Reduction of promoted and unpromoted systems was also monitored through XPS, and Pt was seen to increase the extent of cobalt Reduction by a factor of two.

  • fischer tropsch synthesis study of the promotion of re on the Reduction Property of co al2o3 catalysts by in situ exafs xanes of co k and re liii edges and xps
    Applied Catalysis A-general, 2004
    Co-Authors: Gary Jacobs, John A Chaney, Patricia M Patterson, Tapan K Das, Burtron H Davis
    Abstract:

    A direct relationship between the Fischer–Tropsch synthesis (FTS) rate and the number of surface cobalt atoms available for reaction is usually obtained. For Co/Al2O3 catalysts in particular, the site density depends on two primary factors: (1) the average size of the cobalt clusters on the support; and (2) the fraction of cobalt reduced to the metallic state. The addition of small amounts of noble metal promoters, such as Pt and Ru to cobalt alumina, may catalyze the Reduction of cobalt oxide shifting the temperature of Reduction of both steps (Co3O4→CoO and CoO→Co0) to lower temperatures. However, Re affects only the second step. Re is reduced at a higher temperature than Pt or Ru, and at approximately the same temperature as the first step of cobalt Reduction (Co3O4→CoO). Thus, Re metal is present to catalyze only the second step. In situ extended X-ray absorption fine structure (EXAFS) at the LIII edge of Re has been used to show that there is direct contact of Re with cobalt atoms, while evidence for ReRe bonds is not observed. Even though direct atom-to-atom contact is found, temperature-programmed Reduction (TPR) suggests that hydrogen spillover from the promoter to cobalt oxide clusters is important for the catalysis of cobalt oxide Reduction. In situ EXAFS at the K edge of Co shows that the average cobalt cluster size decreases with increasing Re loading. Re promotes Reduction of smaller species which interact with the support, and therefore, for a given Reduction temperature, the average cobalt metal cluster size decreases as a function of increasing Re content. After Reduction at a temperature slightly above the first peak in the TPR (Co3O4→CoO), the species remaining on the surface displayed XANES spectra identical to that of CoO. After Reduction at a temperature above the second broad TPR peak, XPS showed that a residual oxide species was present, with a binding energy equivalent to cobalt aluminate.

Mojtaba Ahmadieh Khanesar - One of the best experts on this subject based on the ideXlab platform.

  • analysis of the noise Reduction Property of type 2 fuzzy logic systems using a novel type 2 membership function
    Systems Man and Cybernetics, 2011
    Co-Authors: Mojtaba Ahmadieh Khanesar, Mohammad Teshnehlab, Erdal Kayacan, Okyay Kaynak
    Abstract:

    In this paper, the noise Reduction Property of type-2 fuzzy logic (FL) systems (FLSs) (T2FLSs) that use a novel type-2 fuzzy membership function is studied. The proposed type-2 membership function has certain values on both ends of the support and the kernel and some uncertain values for the other values of the support. The parameter tuning rules of a T2FLS that uses such a membership function are derived using the gradient descend learning algorithm. There exist a number of papers in the literature that claim that the performance of T2FLSs is better than type-1 FLSs under noisy conditions, and the claim is tried to be justified by simulation studies only for some specific systems. In this paper, a simpler T2FLS is considered with the novel membership function proposed in which the effect of input noise in the rule base is shown numerically in a general way. The proposed type-2 fuzzy neuro structure is tested on different input-output data sets, and it is shown that the T2FLS with the proposed novel membership function has better noise Reduction Property when compared to the type-1 counterparts.

  • a novel type 2 fuzzy membership function application to the prediction of noisy data
    International Conference on Computational Intelligence for Measurement Systems and Applications, 2010
    Co-Authors: Mojtaba Ahmadieh Khanesar, Mohammad Teshnehlab, Erdal Kayacan, Okyay Kaynak
    Abstract:

    A novel, diamond-shaped type-2 fuzzy member- ship function is introduced in this study. The proposed type-2 fuzzy membership function has certain values on 0 and 1, but it has some uncertainties for the other membership values. It has been shown that the type-2 fuzzy system using this type of membership function introduced in this study has some noise Reduction Property in the presence of noisy inputs. The appropriate parameter selection to be able to achieve noise Reduction Property is also considered. A hybrid method consisting of particle swarm optimization (PSO) and gradient descent (GD) algorithm is used to optimize the parameters of the proposed type-2 fuzzy system. PSO is a derivative-free optimizer, and the possibility of the entrapment of this optimizer in local minimums is less than the gradient descent method. The proposed type-2 fuzzy system and the hybrid parameter estimation method are then tested on the prediction of a noisy, chaotic dynamical system. The simulation results show that the type-2 fuzzy predictor with the proposed novel membership functions shows a superior performance when compared to the other existing type-2 fuzzy systems in the presence of noisy inputs.