The literature treating mechanisms of catalyst deactivation is reviewed. Intrinsic mechanisms of catalyst deactivation are many; nevertheless, they can be classified into six distinct types: (i) poisoning, (ii) fouling, (iii) thermal degradation, (iv) vapor compound formation accompanied by transport, (v) vapor-solid and/or solid-solid reactions, and (vi) attrition/crushing. As (i), (iv), and (v) are chemical in nature and (ii) and (v) are mechanical, the causes of deactivation are basically three-fold: chemical, mechanical and thermal. Each of these six mechanisms is defined and its features are illustrated by data and examples from the literature. The status of knowledge and needs for further work are also summarized for each type of deactivation mechanism. The development during the past two decades of more sophisticated surface spectroscopies and powerful computer technologies provides opportunities for obtaining substantially better understanding of deactivation mechanisms and building this understanding into comprehensive mathematical models that will enable more effective design and optimization of processes involving deactivating catalysts. © 2001 Elsevier Science B.V. All rights reserved.

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Mechanisms of catalyst deactivation

Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.

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Heterogeneous Catalyst Deactivation and Regeneration: A Review

Crystalline structure analysis of cellulose treated with sodium hydroxide and carbon dioxide by means of X-ray diffraction and FTIR spectroscopy.

FTIR analysis of cellulose treated with sodium hydroxide and carbon dioxide.

A technique is described for fabricating arrays of uniform CdS nanowires with lengths up to 1 μm and diameters as small as 9 nm by electrochemically depositing the semiconductor directly into the pores of anodic aluminum oxide films from an electrolyte containing Cd2+ and S in dimethyl sulfoxide. The nanowire arrays were characterized by powder X-ray diffraction (XRD) and electron microscopy. The deposited material is found to be hexagonal CdS with the crystallographic c-axis preferentially oriented along the length of the pore. The effects of annealing on the crystallinity of the deposited semiconductor were investigated by XRD and resonance Raman spectroscopy. The deposition technique is, in principle, generalizable as a means of fabricating nanowires of a wide range of semiconductors.

Electrochemical Fabrication of CdS Nanowire Arrays in Porous Anodic Aluminum Oxide Templates

FT-IR and FT-Raman study of hydrothermally degradated cellulose

http://www2.chemia.uj.edu.pl/~proniewi/pdf/publ70.pdf

FT-IR and FT-Raman study of hydrothermally degraded groundwood containing paper

The structural characteristics of films cathodically electrodeposited from a dimethylsulfoxide solution containing cadmium chloride and elemental sulfur have been studied. The thickness, continuity, smoothness, and the degree of substrate coverage of the films have been examined using stylustype surface profiling techniques, x‐ray diffractometer patterns, and scanning electron microscopy. The composition of the films was examined using Rutherford backscattering spectrometry. It is concluded that high quality films of with a high degree of crystal structure can be electrodeposited in this manner and that minority components may be easily incorporated in the films.

The Structural Characterization of Cadmium Sulfide Films Grown by Cathodic Electrodeposition

Well‐characterized catalyst model compounds of KAlO2 and KFeO2 are investigated by thermal desorption of potassium from the material. The desorbing fluxes of ions, atoms and highly excited states (field ionizable Rydberg states) were studied with surface and field ionization detectors in a vacuum apparatus. From the Arrhenius plots the activation energies for desorption of K and K+ were determined. The chemical state of potassium at the surfaces is concluded to be: ionic on KAlO2 (with the K desorption barrier of 1.76 eV) and covalent on KFeO2 (barrier of 2.73 eV). These results agree with the data obtained earlier for industrial catalysts for ammonia and styrene production. They are interpreted in terms of the Schottky cycle, which is completed for KAlO2 and fails for KFeO2. This failure indicates a non‐equilibrium desorption process. K Rydberg states are only found to desorb from KFeO2, in agreement with the suggestion that such states in some way are responsible for the catalytic activity.

Stability and excitation of potassium promoter in iron catalysts - the role of KFeO2 and KAlO2 phases

Non-destructive methods of sampling during the physicochemical studies of historical objects such as old books and manuscripts seem to be an obvious choice. Since furfural has been shown to be one of the most abundant gaseous products of cellulose degradation, it can be considered as a convenient marker of degradation progress. The number of quantitative data concerning correlations between the emission of furfural and physicochemical and mechanical properties of paper is rather scarce in the literature. In the present studies, a model paper containing more than 99% of cellulose was aged inside closed vials at 90°C. Gaseous products of paper degradation were measured using sorption tubes filled with Tenax TA sorbent and GC-MS. The method has proved to be sufficiently sensitive for measuring furfural emission not only in accelerated degradation at 90°C but also during natural ageing of paper at room temperature even in relatively short time intervals of 2–28 days. The correlations between furfural emission and polymerization degree, pH, color, tear index, number of double folds and breaking length have been statistically confirmed at confidence level α=0.001. Basing on them it was possible to estimate the number of broken glycosidic bonds per one molecule of furfural formed during degradation—we found a value equal to 9.2.

Andrzej Barański

Papers

FT-IR and FT-Raman study of hydrothermally degradated cellulose

FT-IR and FT-Raman study of hydrothermally degraded groundwood containing paper

The Structural Characterization of Cadmium Sulfide Films Grown by Cathodic Electrodeposition

Stability and excitation of potassium promoter in iron catalysts - the role of KFeO2 and KAlO2 phases

Furfural as a marker of cellulose degradation. A quantitative approach