Catalyst characterization procedure

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. 

Catalysts Characterization Catalysts were characterized by nitrogen adsorption-desorption isotherms, XRD, XPS, TEM, and FT-IR. The concentration and the strength of the acid sites were determined using a combination of NHs-chemisorption and FTIR. Detailed procedures are given elsewhere [18, 19]. 

The experimental apparatus has been described in detail elsewhere (11,12,22). In previous communications we have also described the porous silver catalyst film deposition and characterization procedure (11,12). Ten different reactor-cells were used in the present investigation. The cells differed in the silver catalyst surface area as shown in Table I. Catalysts 2 through 5 had been also used in a previous study (17). The reactor-cells also differed in the zirconia electrolyte thickness which could not be measured accurately. The electrolyte thickness varies roughly between 150 and 300 ym. 

Httckel procedure, 25 35 of hydrocarbons, 26 28-39 hydrogen, 30 243-248 catalyst characterization by, 23 14-16 and hydrogenolysis of hydrocarbons, 23 92 interaction wilb simple molecules, 34 147-149... 

By following this multistep procedure, the kinetics were evaluated on a wide range of data (both conditions and feedstock) not used in the parameter estimation. The start-of-cycle kinetics were extended to other catalysts and catalyst states by defining an appropriate catalyst state vector (a = aD, al5 a , ac), which is different from 1 at the start of cycle. A catalyst characterization test was developed to estimate parameters for new catalysts. 

With improvements in the preparation of more active HDS catalysts, MoS2 crystallites became smaller, and traditional physical techniques for characterization such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) became limited. In fact, today s best catalysts do not exhibit XRD patterns, and the active catalyst particles can no longer be observed directly by TEM. Thus, new techniques were required to provide structural information about Co(Ni)-Mo-S catalysts. As modern surface science characterization procedures evolved, they were immediately applied to the study of CoMoSx-based... 

The performance of a catalyst is well known to be sensitive to its preparation procedure. For this reason, ideally an oxide-supported metal catalyst should be subjected to a number of characterization procedures. These may include measurements of the metal loading within the overall catalyst (usually expressed in wt%), the degree of metal dispersion (the proportion of metal atoms in the particle surfaces), the mean value and the distribution of metal particle diameters, and qualitative assessments of morphology including the particle shapes and evidence for crystallinity. These properties in turn can depend on experimental variables used in the preparation, such as the choice and amounts of originating metal salts, prereduction, calcination or oxygen treatments, and the temperature and duration of hydrogen reduction procedures. 

Thus, in order to determine the processability of petroleum a series of consistent and standardized characterization procedures are required (ASTM, 1995). These procedures can be used with a wide variety of feedstocks to develop a general approach to predict processability. The ability to predict the outcome of feedstock (especially heavy oils and residua) processing offers (1) the choice of processing sequences (2) the potential for coke lay-down on the catalyst (3) determining the catalyst tolerance to different feedstocks (4) predictability of product distribution and quality and (5) incompatibility during processing and incompatibility of the products on storage. 

The experimental apparatus and the silver catalyst preparation and characterization procedure is described in detail elsewhere (10). The porous catalyst film had a superficial surface area of 2 cm2 and could adsorb approximately (2 +. 5) 10-b moles O2 as determined by oxygen chemisorption followed by titration with ethylene (10). The reactor had a volume of 30 cm3and over the range of flowrates used behaved as a well mixed reactor (10, 11). Further experimental details are given in references (10) and (11). 

This manual provides definitions and recommendations concerning the terminology of catalysts. It should be read in conjunction with the Manual of Methods and Procedures for Catalyst Characterization which provides details and recommendations concerning the experimental methods used in catalysis. 

This manual has been prepared by the Commission on Colloid and Surface Chemistry including Catalysis of the IUPAC. It complements the Manual on Catalyst Characterisation which concerned nomenclature [1] and should be read in conjunction with this earlier manual. The Manual of Methods and Procedures for Catalyst Characterization provides details and recommendations concerning the experimental methods used in catalysis. The objective is to provide recommendations on methodology (rational approaches to preparation and measurements). It is not intended to provide specific methods of preparation or measurement, nor is it concerned with terminology, nomenclature, or standardization. 

The first chapter (Chapter 10) in the section on catalyst characterization summarizes the most common spectroscopic techniques used for the characterization of heterogeneous catalysts, such as XPS, Auger, EXAFS, etc. Temperature programmed techniques, which have found widespread application in heterogeneous catalysis both in catalyst characterization and the simulation of pretreatment procedures, are discussed in Chapter 11. A discussion of texture measurements, theory and application, concludes the section on the characterization of solid catalysts (Chapter 12). 

As can be seen, the field of catalyst characterization makes extensive use of most available chemical testing methodologies, and requires the cooperation and collaboration of many different people to be successful. Due to the complexity of catalyst preparation and use, it is not surprising that different laboratories have developed different methods and procedures to measure the same property. 

Characterization of Metal Sites on Supported Metal Catalysts. Characterization of supported metals is usually more difficult. Considerable variation can frequently be found in the state of the reduced metal as a result of apparently minor differences in pretreatment, impurities in the support, or residual water or other contaminants. The problem is most severe with readily oxidizable metals. Ni (10), Mo (11), Re (12) and other metals can all show major variations depending on sample pretreatment and reduction procedures. Even in the case of platinum group metals many complications exist. The frequencies of bands observed when CO is adsorbed in a given manner (e.g. "linear" or "bridged") can shift by up to 100 cm 1 with coverage by CO or between different samples. 

To achieve these criteria, we needed to establish standard processing and characterization procedures for FCC catalysts. In particular, a process for making microspheres of controlled size distribution and shape, independent of composition, had to be defined. Also, an approach for obtaining the intrinsic attrition rate of commercial grade and experimental catalysts had to be adapted from a method for alumina. This paper describes these methods and shows that the substitution of CP alumina for part of the clay in a commercially viable FCC formulation can improve attrition behavior and enhance catalytic activity, especially in the presence of Ni+V poisoning. 

Subsequent investigations, including IINS, were carried out to characterize the various resistances of such cokes to controlled after-treatments, such as oxidation or hydrogasification processes, as a basis for determining the feasibility of catalyst reactivation. The presence of metallic contaminants (iron, cobalt, and nickel) was of relevance, not only to the deposition of cokes and the catalytic transformation of the carbon structure, but also to the dynamic processes in the controlled decomposition of the material in catalyst regeneration procedures 50). 

Catalyst Characterization. Chemical analyses, x-ray diifraction analyses, and gas adsorption procedures were used to characterize the composition, crystallographic character, and surface structure of the nickel and cobalt zeolite catalyst preparations. The chemical and x-ray procedures were standard methods with the latter described elsewhere 11). Carbon monoxide chemisorption measurements provide useful estimates of the surface covered by nickel atoms from the zeolite substrate 10). 

To assess about the quality and purity of the synthesized membranes, several experimental techniques and procedures are available many of those are commonly employed in catalyst characterization. Thus, XRD (x-ray diffraction) analysis of the supported samples is conventionally used to identify the type of zeolite, the proportion of amorphous material and impurities, and the preferential orientation of the crystals (XRD-pole figure). However, for the vast majority of the synthesis procedures described, the XRD spectra of the scrapped membrane or the resulting powder from the liquid phase is supplied to avoid the support contribution. 

Catalyst characterization and mimicking pretreatment procedures by temperature-programmed techniques... 

Different mbted Ir-Mo/alumina catalysts were prepared. The details of procedures and catalyst characterization were published elsewhere [10,11]. In the first series, the Mo was deposited first. The samples were prepared from Mo03/alumina or MoS2/alumina catalyst by adsorption of Ir4(CO)i2 from a cyclohexane solution. This procedure was the same as for the Ir catalysts. In another series, an inverse order of impregnation was used. The Ir was deposited first and then Mo was deposited from an aqueous solution of AHM. One catalyst was prepared by coimpregnation of alumina by an aqueous solution of AHM and (NH4)2lrCl6. The samples containing Ir were sulfided or reduced without calcination in air in order to avoid Ir sintering. The surface areas of mixed catalysts varied between 200-208 m /g. 

Catalyst characterization. The extraction procedure removed all of the remaining unchanged precursors from the zeolite surflice. The uncomplexed cobalt ions were re-exchanged, using saturated NaCl solution. Thus, all the residual cobalt present is associated with encaged cobalt(salophen). 

Yields and kinetics depend on the type and number of Ti species and the crystal size of the catalyst used. Ti distribution between lattice (selective) and extra-lattice (unselective) sites is, in turn, closely linked to synthesis and characterization procedures, both of which require special thoroughness [4]. Inadequate characterization and, therefore, the impossibility of clear assessment of siting of Ti in the catalyst, is a frequent obstacle to a correct evaluation of the literature, especially early publications. These considerations are of general value, but are central to the hydroxylation of phenol where extra-framework species are a major source of hydrogen peroxide decomposition and radical chain oxidations. The hydroxylation of phenol was indeed proposed by three different groups as an additional test to assess the purity of TS-1 [2, 9, 11]. Van der Pool et al. estimated from Weisz... 

Sulfided samples were characterized with XRD, BET surface area, NO sorption capacity, ESR and FTIR spectroscopy. The details concerning the characterization procedures as well as certain properties of USY based samples can be found elsewhere (ref. 9, 10). The ammonia adsorption capacity of sulfided and non-sulfided catalysts and supports was measured from the desorption peak obtained during 3the temperature programmed desorption (heating rate 30 K min ). Each sample (0.1 g) after activation or sulfidation was saturated with ammonia (a series of 1 cm NH3 injections) at 375 K until full saturation was achieved. This was monitored as a sharp GC peak detected by thermal conductivity detector. Next, sample was purged 1 hour in purified helium at 375 K to remove the excess of weakly held ammonia and TPD started. 

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