Catalyst physical characterization

Spengler, ]. Anderle, F. Bosch, E. Grasselli, R. K. Pillep, B. Behrens, R Lapina, O. B. Shubin, A. A. Eberle, H. ]. Knozinger, H. Antimony Oxide-Modified Vanadia-Based Catalysts—Physical Characterization and Catalytic Properties. J. Phys. Chem. B 2001, 105, 10772-10783. 

Important physical properties of catalysts include the particle size and shape, surface area, pore volume, pore size distribution, and strength to resist cmshing and abrasion. Measurements of catalyst physical properties (43) are routine and often automated. Pores with diameters <2.0 nm are called micropores those with diameters between 2.0 and 5.0 nm are called mesopores and those with diameters >5.0 nm are called macropores. Pore volumes and pore size distributions are measured by mercury penetration and by N2 adsorption. Mercury is forced into the pores under pressure entry into a pore is opposed by surface tension. For example, a pressure of about 71 MPa (700 atm) is required to fill a pore with a diameter of 10 nm. The amount of uptake as a function of pressure determines the pore size distribution of the larger pores (44). In complementary experiments, the sizes of the smallest pores (those 1 to 20 nm in diameter) are deterrnined by measurements characterizing desorption of N2 from the catalyst. The basis for the measurement is the capillary condensation that occurs in small pores at pressures less than the vapor pressure of the adsorbed nitrogen. The smaller the diameter of the pore, the greater the lowering of the vapor pressure of the Hquid in it. 

The hterature consists of patents, books, journals, and trade Hterature. The examples in patents may be especially valuable. The primary Hterature provides much catalyst performance data, but there is a lack of quantitative results characterizing the performance of industrial catalysts under industrially reaHstic conditions. Characterizations of industrial catalysts are often restricted to physical characterizations and perhaps activity measurements with pure component feeds, but it is extremely rare to find data characterizing long-term catalyst performance with impure, multicomponent industrial feedstocks. Catalyst regeneration procedures are scarcely reported. Those who have proprietary technology are normally reluctant to make it known. Readers should be critical in assessing published work that claims a relevance to technology. 

For more than five decades, the methods of surface physics and chemistry have provided some of the most incisive results advancing our understanding of the catalytic action of solids at the molecular scale. Characterizations by physical methods have demonstrated the dynamic nature of catalyst surfaces, showing that their structures, compositions, and reactivities may all be sensitive to temperature and the composition of the reactive environment. Thus, the most insightful catalyst characterizations are those of catalysts as they function. This volume of Advances in Catalysis is dedicated to the topic of physical characterization of solid catalysts in the functioning state. Because the literature of this topic has become so extensive, the representation will extend beyond the present volume to the subsequent two volumes of the Advances. 

The growing interest in physical characterization of solid catalysts as they function has stimulated a new series of congresses, the first held in Lunteren (The Netherlands) in 2003 and the second in Toledo in 2006. The subject has been documented in recent books (B. M. Weckhuysen, Ed., In situ Spectroscopy of Catalysts, American Scientific Publishers, 2004, and J. F. Haw, Ed., In situ Spectroscopy in Heterogeneous Catalysis, Wiley-VCH, 2002) and in topical issues of journals Top. Catal. 15 (2001) Phys. Chem. Chem. Phys. 5, issue 20 (2003) and Catal. Today 113 (2006). It is our intention that our set of volumes be more nearly comprehensive than these publications, as well as providing many newer results. 

Niobium- and tantalum-containing mesoporous molecular sieves MCM-41 have been studied by X-ray powder diffraction, 29Si MAS NMR, electron spin resonance, nitrogen adsorption and UV-Vis spectroscopy and compared with niobium- and tantalum-containing silicalite-1. The results of the physical characterization indicate that it is possible to prepare niobium- and tantalum-containing MCM-41 and silicalite-1, where isolated Nb(V) or Ta(V) species are connected to framework defect sites via formation of Nb-O-Si and Ta-O-Si bonds. The results of this study allow the preparation of microporous and mesoporous molecular sieves with remarkable redox properties (as revealed by ESR), making them potential catalysts for oxidation reactions. 

FIGURE 9.17 Physical characterization of a 30% Pt09Sn01/C catalyst with 30wt% metal loading prepared with the Bonnemann method (a) TEM image and (b) particle size distribution. 

EUROPT-1 is a silica-supported platinum catalyst containing 6.3 %Pt [1—8a]. This unusually high metal loading was chosen in order to facilitate the use of as many techniques of characterization as possible (see discussion following Ref. 8a) in particular, it is difficult to apply electron microscopy if the metal content is less than 1%. Samples were distributed to some 20 members of EUROCAT, and detailed results on its physical characterization were reported in five papers [1-5] and summaries presented in two conference proceedings [8a, 9a]. Results concerning its catalytic behavior were published later [6], and most recently a comprehensive review of work performed by other users of the catalyst has appeared [7], Publications describing its use continue to appear. 

Catalysts which have been heated for one hour at 250°C. with carbon monoxide at 100 mm., cooled to 35°C., and pumped to remove physically adsorbed gas have far greater activities than untreated catalysts at all chromium concentrations (7). At low pressures, CO treatment increases the activity by at least an order of magnitude. As described in a previous publication, on the basis of infrared evidence, it is believed that the CO-treated catalyst is characterized by the presence of a carbon monoxide-chromium complex. 

Volumes 50 and 51 of the Advances, published in 2006 and 2007, respectively, were the first of a set of three focused on the physical characterization of solid catalysts in the functioning state. This volume completes the set. The six chapters presented here are largely focused on the determination of structures and electronic properties of components and surfaces of solid catalysts. The first chapter is devoted to photoluminescense spectroscopy it is followed by chapters on Raman spectroscopy ultraviolet-visible-near infrared (UV-vis-NIR) spectroscopy X-ray photoelectron spectroscopy X-ray diffraction and X-ray absorption spectroscopy. 

Colloidal Semiconductors in Systems for the Sacrificial Photolysis of Water. 1. Preparation of a Pt/Ti02 Catalyst by Heterocoagulation and its Physical Characterization 254... 

Electron microscopy, with its high spatial resolution, plays an important role in the physical characterization of these catalysts. Scanning electron microscopy (SEM) is used to characterize the molecular sieve particle sizes and morphologies as a function of preparation conditions. Transmission electron microscopy (TEM) is used to follow the changes in the microstructure of the iron silicates caused by different growth conditions and subsequent thermal and hydrothermal treatments. 

Several experimental methods are available to characterize catalyst pore structure. Some of them, useful in quantifying mass transfer of reactant and product inside the porous particle, will be only briefly discussed here. More details concerning methods for the physical characterization of porous substances are given by various authors [5,8,9],... 

Volume 50 of Advances in Catalysis, published in 2006, was the hrst of a set of three focused on physical characterization of solid catalysts in the functioning state. This volume is the second in the set. The hrst four chapters are devoted to vibrational spectroscopies, including Fourier transform infrared (Lamberti et al.), ultraviolet Raman (Stair), inelastic neutron scattering (Albers and Parker), and infrared-visible sum frequency generation and polarization-modulation infrared rehection absorption (Rupprechter). Additional chapters deal with electron paramagnetic resonance (EPR) (Bruckner) and Mossbauer spectroscopies (Millet) and oscillating microbalance catalytic reactors (Chen et al.). 

In order to assess the viability of quantitative XPS as a tool in the physical characterization of coke deposits, we have studied a number of spent catalysts which contained considerable amounts of coke. The spent heavy-oll -processing catalysts were obtained from vacuum gas oil hydroconver ion experiments. The activity of fresh and spent catalysts was evaluated from thiophene hydrodesulfurization tests. 

Catalysts regenerated by methods (A) and (B) are evaluated on the basis of bench-scale activity tests, characterization of catalyst physical and chemical properties, and physical integrity tests, such as particle attrition resistance,... 

Abstract Immobilized metallic and bimetallic complexes and clusters on oxide or zeolite supports made from well-defined molecular organometaUic precursors have drawn wide attention because of their novel size-dependent properties and their potential applications for catalysis. It is speculated that nearly molecular supported catalysts may combine the high activity and selectivity of homogenous catalysts with the ease of separation and robustness of operation of heterogeneous catalysts. This chapter is a review of the synthesis and physical characterization of metaUic and bimetallic complexes and clusters supported on metal oxides and zeohtes prepared from organometaUic precursors of well-defined molecularity and stoichiometry. 

Basset J-M, Lefebvre F, Santini C (1998) Surface organometallic chemistry Some fundamental features including the coordination effects of the support. Coord Chem Rev 178-180 1703 Gates BC (2000) Supported metal cluster catalysts. J Mol Catal A Chem 163 55 Fierro-Gonzalez JC, Kuba S, Hao Y, Gates BC (2006) Oxide- and zeoUte-supported molecular metal complexes and clusters Physical characterization and determination of structure, bonding, and metal oxidation state. J Phys Chem B 110 13326... 

In this chapter we review studies, primarily from our laboratory, of Pt and Pt-bimetallic nanoparticle electrocatalysts for the oxygen reduction reaction (ORR) and the electrochemical oxidation of H2 (HOR) and H2/CO mixtures in aqueous electrolytes at 274—333 K. We focus on the study of both the structure sensitivity of the reactions as gleaned from studies of the bulk (bi) metallic surfaces and the resultant crystallite size effect expected or observed when the catalyst is of nanoscale dimension. Physical characterization of the nanoparticles by high-resolution transmission electron microscopy (HRTEM) techniques is shown to be an essential tool for these studies. Comparison with well-characterized model surfaces have revealed only a few nanoparticle anomalies, although the number of bimetallics... 

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