Enhanced resolution of ultra micropore size determination of biochars and activated carbons by dual gas analysis using N2 and CO2 with 2D-NLDFT adsorption models

International audienc

Preparation and characterization of dispersed copper on silica as model catalysts

Ph.D.Mark G. Whit

On the Application of an In Situ Catalyst Characterization System (ICCS) and a Mass Spectrometer Detector as Powerful Techniques for the Characterization of Catalysts

The in situ characterization of catalysts provides important information on the catalyst and the understanding of its catalytic performance and selectivity for a specific reaction. Temperature programmed analyses (TPX) techniques for catalyst characterization reveal the role of the support on the stabilization and dispersion of the active sites. However, these can be altered at high temperatures since sintering of active species can occur as well as possible carbon deposition which hinders the active species and deactivates the catalyst. The in situ characterization of the spent catalyst, however, may expose the causes of catalyst deactivation. For example, a simple temperature programmed oxidation (TPO) analysis on the spent catalyst may produce CO and CO2 via a reaction with O2 at high temperatures and this is a strong indication that deactivation may be due to the deposition of carbon. Other TPX techniques such as temperature programmed reduction (TPR) and pulse chemisorption are also valuable techniques when they are applied in situ to the fresh catalyst and then to the catalyst upon deactivation. In this work, two Ni supported catalysts were considered as examples to elucidate the importance of these techniques in the characterization study of catalysts applied to the reaction of hydrogenation of CO2

Exploiting In-Situ Characterization for a Sabatier Reaction to Reveal Catalytic Details

In situ characterization of catalysts provides important information on the catalyst and the understanding of its activity and selectivity for a specific reaction. TPX techniques for catalyst characterization reveal the role of the support on the stabilization and dispersion of the active sites. However, these can be altered at high temperature since sintering of active species can occur as well as possible carbon deposition through the Bosch reaction, which hinders the active species and deactivates the catalyst. In situ characterization of the spent catalyst, however, may expose the causes for catalyst deactivation. For example, a simple TPO analysis on the spent catalyst may produce CO and CO2 via a reaction with O2 at high temperature and this is a strong indication that deactivation may be due to the deposition of carbon during the Sabatier reaction. Other TPX techniques such as TPR and pulse chemisorption are also valuable techniques when they are applied in situ to the fresh catalyst and then to the catalyst upon deactivation

High Oxygen Nanocomposite Barrier Films based on Xylan and Nanocrystalline Cellulose

The goal of this work is to produce nanocomposite film with low oxygen permeability by casting an aqueous solution containing xylan, sorbitol and nanocrystalline cellulose. The morphology of the resulting nanocomposite films was examined by scanning electron microscopy and atomic force microscopy which showed that control films containing xylan and sorbitol had a more open structure as compared to xylan-sorbitol films containing sulfonated nanocrystalline cellulose. The average pore diameter, bulk density, porosity and tortuosity factor measurements of control xylan films and nanocomposite xylan films were examined by mercury intrusion porosimetry techniques. Xylan films reinforced with nanocrystalline cellulose were denser and exhibited higher tortuosity factor than the control xylan films. Control xylan films had average pore diameter, bulk density, porosity and tortuosity factor of 0.1730 μm, 0.6165 g/ml, 53.0161 % and 1.258, respectively as compared to xylan films reinforced with 50 % nanocrystalline cellulose with average pore diameter of 0.0581 μm, bulk density of 1.1513 g/ml, porosity of 22.8906 % and tortuosity factor of 2.005. Oxygen transmission rate tests demonstrated that films prepared with xylan, sorbitol and 5%, 10%, 25% and 50 % sulfonated nanocrystalline cellulose exhibited a significantly reduced oxygen permeability of 1.1387, 1.0933, 0.8986 and 0.1799 cm 3 ⋅μm/m 2 ⋅d⋅kPa respectively with respect to films prepared solely from xylan and sorbitol with a oxygen permeability of 189.1665 cm 3 ⋅μm/m 2 ⋅d⋅kPa. These properties suggested these nanocomposite films have promising barrier properties

Using a New Finite Slit Pore Model for NLDFT Analysis of Carbon Pore Structure

In this work, we present a model for analyzing activated carbon micropore structures based on graphene sheet walls of finite thickness and extent. This is a two-dimensional modification of the widely used infinite slit pore model that assumes graphite-like infinitely extended pore walls. The proposed model has two versions: (1) a strip pore constructed with graphene strip walls that have a finite length L in the x-direction and are infinite in the y-direction. Strip pores are open on both sides in the x-direction; (2) a channel pore, i.e. a strip pore partially closed along one edge by a perpendicularly orientated graphene wall. This more realistic model allows pore termination via both physical pore entrances and pore blockage. The model consequently introduces heterogeneity of the adsorption potential that is reduced near pore entrances and enhanced near the corners of pore walls. These energetically heterogeneous structures fill with adsorbate more gradually than homogeneous pores of the same width. As a result, the calculated adsorption isotherms are smoother and less steep for the finite versus the infinite pore model. In the application of this model for carbon characterization, it is necessary to make an assumption about the pore length. In this work, we made this assumption based on high-resolution scanning transmission electron microscopy (STEM) results. We find the agreement between the experiment and the model significantly better for the finite than for the infinite pore model

Monte Carlo simulation and experimental studies on the low temperature characterization of nitrogen adsorption on graphite

Adsorption of nitrogen is commonly used to characterise porous carbon solids, and an important prerequisite for a good characterization is that the molecular model for nitrogen should give the correct description of adsorption on a graphite surface over a range of temperatures. To investigate the role of the molecular shape and quadrupole of nitrogen at temperatures below the boiling point we carried out a comprehensive molecular simulation study of the performance of two popular molecular models for nitrogen: (1) 1-site LJ model (1CLJ) and (2) a model with two LJ sites and three partial charges (2CLJ+3q). It was found that, although the 2CLJ+3q model generally gave a better description of the isotherms than the 1CLJ model, when used in Grand Canonical Monte Carlo simulations, it was not able to account for the known spike in the heat curve versus loading at 77 K. When the simulations were re-run in the recently introduced Bin-MC scheme in a canonical ensemble better agreement was found between simulation results and the experimental data for the 2CLJ+3q model over a wide range of temperatures; a result that has not been previously reported in the literature. (C) 2012 Elsevier Ltd. All rights reserved

Structural analysis of hierarchically organized zeolites

Advances in materials synthesis bring about many opportunities for technological applications, but are often accompanied by unprecedented complexity. This is clearly illustrated by the case of hierarchically organized zeolite catalysts, a class of crystalline microporous solids that has been revolutionized by the engineering of multilevel pore architectures, which combine unique chemical functionality with efficient molecular transport. Three key attributes, the crystal, the pore and the active site structure, can be expected to dominate the design process. This review examines the adequacy of the palette of techniques applied to characterize these distinguishing features and their catalytic impact.ISSN:2041-172

Assessment of the Reaction Location of Skeletal 1‑Butene Isomerization over Ferrierite

The pore accessibility of fresh and spent ferrierite (FER) during skeletal 1-butene isomerization is assessed via probe molecule adsorption. Argon and nitrogen adsorption isotherms demonstrate that micropores become inaccessible within 24 h. Despite this, the catalyst remains active over 200 h and the yield of iso-butene continues to increase during the initial 100 h. Butene and toluene adsorption isotherms show that only small, linear hydrocarbons (kinetic diameter <5 Å) can enter the catalyst pore network. Hence, the pore size of FER is vital for this reaction due to the immobilization of catalytically active carbonaceous deposits at the pore mouths rather than shape selectivity