Morphology studies, catalysts

Boehm, H.P. "Carbon from Carbon Monoxide Disproportionation on Nickel and Iron Catalysts Morphological Studies and Possible Growth Mechanisms" Carbon 1973, 11, 583. 

High resolution electron microscopy has recently demonstrated the capability to directly resolve the atomic structure of surfaces on small particles and thin films. In this paper we briefly review experimental observations for gold (110) and (111) surfacest and analyse how these results when combined with theoretical and experimental morphological studies, influence the interpretation of geometrical catalytic effects and the transfer of bulk surface experimental data to heterogeneous catalysts. 

Future challenges for polymerization model catalysts include studying the structure of polymers below their melting point, in what is termed the nascent morphology. Such studies can either be undertaken on silica-supported chromium catalysts (as discussed above), or on so-called single-site catalysts, such as metallocenes, applied on flat silica supports. 

In this review the intrinsic kinetic aspects are dealt with in the first place The progressive coverage of active sites of the catalyst, which affects its activity and the process selectivity, is cast in a mechanistic form. These kinetic aspects are then studied in combination with the influence of the catalyst morphology, first at the pore level, then at the particle level, seen as a network of pores. Next, growth of coke, leading eventually to pore blcx kage and diffusional limitations are introduced The practical application of the models in kinetic studies is given particular attention. Finally, the effect of catalyst deactivation on the behavior of the reactor is discussed. 

The morphology of the carbonaceous deposits generated by the decomposition of propane on the nickel and nickel-potassium catalysts was studied by TEH. It was found that the reaction of propane, at elevated temperatures (375 0-500 0, produced filamentary carbon on the catalysts. These filaments were hollow, 100A-900A in diameter and had highly orientated nickel crystallites at the top,... 

Work is in progress to determine to what extent a Ru particle size effect is controlling catalyst performance (ie is there a structure sensitivity) and to what extent the nature of the initial Rug CO -oxide interaction and differences in the surface crystallography of the particular oxides are contributory factors. Morphological studies by TEM and electron diffraction as well as detailed FTIR and ESCA studies are currently addressing these problems. 

Effect of Surface Morphology on the Adsorption States of CO Over Ru/Ti02 and RU/AI2O3 Catalysts FTIR Study... 

The process involves transesterification (catalyst, 200 °C) followed by polycondensation (250 °C, second stage. Morphological studies show the presence of crystalline (mp 190-200 °C) polyester lamellae in a continuous amorphous phase. In contrast to the A-B-A thermoplastic elastomers where the domains are formed from amorphous polystyrene segments, the domains here are formed from crystalline hard segments containing the 1,4-glycol polyester moiety. 

These techniques and their analyses could also be employed to select and refine the models by which deactivation may be analyzed however, to date no studies have employed this extent of techniques in the analysis of catalyst deactivation. Currently, there is a crucial need a combination of the characterization of catalyst morphology and chemistry in concert with modeling of catalyst deactivation. This combined effort should contribute to the development of realistic models and, thereby, pragmatic conclusions as to the understanding and improvement in catalyst performance. 

MPa for a duration in excess of 10 minutes. The prepared wafers have a thickness of approximately 100 to 150 pm, depending on the initial quantity of oxide power used. The systems were thoroughly characterized with several spectroscopic techniques [12,13] to ensure accurate compositional and morphological information. The cerium-zirconium model catalysts were studied to facilitate sulfur deactivation characterization. 

The morphological studies of catalyst systems polymerized for different times revealed that the particle growth starts only after distinctly exceeding the induction period and proceeds continually as the polymerization activity increases. The onset of fragmentation of the support is a prerequisite for the particle growth and the simultaneous conservation of morphology. 

A subsequent detailed investigation of glycerol oxidation has been carried out by Prati et al. in Milano. In a first study, the relationship between catalyst morphology and selectivity was explored at full conversion it was found that larger gold particles (20 nm), supported on suitable carbons, show low TOFs but favour glycerate formation under mild conditions (30 °C, 3 bar) allowing yields up to 92% [39]. 

Studies of size effects in the catalytic activity of support-immobilized metal nanoparticles rely heavily on the ability of researchers to (i) control the average size of the supported nanoparticles, (ii) control and make sure that the particle size distributions are as narrow as possible, and (iii) characterize the catalysts as well as possible (i.e., not omitting challenging to observe ultrasmall particles from the picture) [54]. If the model systems at the laboratory scale are to be seriously considered as candidates for the development of industrially relevant catalysts, then their recyclability and stability under industrial catalytic conditions become crucial. The stability of the catalyst morphology under catalytic testing conditions is also important when size effects are considered, as unwanted effects, such as particle aggregation or metal leaching, may complicate the observed pattern of catalytic activity. 

Small amounts of Ru or Ir were sputter-deposited on Pt-NSTF substrate to determine their stability and OER activity in a fuel cell environment. Ex situ characterization of as-grown material was first performed in order to characterize the morphology and surface state of each OER catalyst. Scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS) were employed to complete this task. Two different OER catalyst loadings were studied, 2 and 10 pg/cm, in order to explore the impact of layer thickness on the catalyst morphology and composition. 

Comparative studies of the aqueous HCl route (designated VPA), the isobutanol route (designated VPO), and the dihydrate route (designated VPD) are shown in Table 7. All three routes give VPO catalysts with similar intrinsic activities [ca. 1.2 X 10 mol maleic anhydride/(m h)] but the surface areas are markedly different. This is a further clear example of the catalyst preparation method controlling the catalyst morphology and activity of the final catalysts. 

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