Catalyst preparation procedure

Copper ore containing a deposit of aurlchalclte was obtained from Wards Natural Science Establishment. The mineral aurlchalclte crystallites were gently scraped from the ore and rinsed In ethanol prior to use. The synthetic precursor was prepared by copreclpltatlon from a mixture of IM Cu and IM Zn nitrate solutions, such that a Cu/Zn mole ratio of 30/70 was prepared, by dropwlse addition of IM Na2C03 at 90 C until the pH Increased from approximately 3 to 7. Calcination and reduction of the mineral were performed as In standard catalyst preparation procedures, which have been described In detail earlier (jL). ... 

The aurlchalclte mineral was calcined In air at 350°C for 4 hours according to the standard catalyst preparation procedure used earlier for the precipitated precursor (1 ). XRD showed that aurlchalclte and... 

Combined analyses by XRD and TEM showed that the aurichalcite mineral was sufficiently similar to the synthetic aurichalcite to be used as a model compound, to study the microstructural changes occurring during the catalyst preparation procedures. Calcination of the mineral and synthetic samples led to highly preferred orientations of ZnO. ZnO electron diffraction patterns with [lOlO] and [3031] zone... 

In summary, large (>lpm) single crystal platelets of aurichalcite produced highly dispersed Cu and ZnO particles with dimensions on the order of 5 nm, as a result of standard catalyst preparation procedures used in the treatment of the precipitate precursors. The overall platelet dimensions were maintained throughout the preparation treatments, but the platelets became porous and polycrystalline to accommodate the changing chemical structure and density of the Cu and Zn components. The morphology of ZnO and Cu in the reduced catalysts appear to be completely determined by the crystallography of aurichalcite. 

According to detailed XRD analyses, the two catalyst preparation procedures under study formed solid solutions. The application of sol-gel method led to improved selectivity to olefins in the reaction of propane ODH, compared to the simple procedure of evaporation and decomposition. However, the propane conversion on the sol-gel catalysts was lower at the same experimental conditions, while the catalysts surface area was higher. Moreover, the sol-gel samples presented higher basicity as shown by C02 TPD. It could be explained by a better incorporation of Nd into the AEO lattice, creating cationic vacancies for attaining electroneutrality and thus rendering the nearby oxide anions coordinatively unsaturated and more basic. 

Bi/Pt atomic ratios (changing from 0.1 to 0.4), as well as the precise preparation procedure of the BiPt/C catalysts, yielded differences in selectivity between glyceric acid, dihydroxyacetone and hydroxypyruvic acid that were not always easy to rationalize [72, 73]. The catalyst preparation procedures using acid-treated carbon (with enhanced number of surface carboxyl groups) are essentially as follows ... 

To focus only on the binary compositions, the catalysts were evaluated under the following experimental conditions feed 40% propylene and 10% oxygen temperature, 250 °C and 20 000 h-1 of GHSV (gas hourly space velocity). Three different catalyst preparation procedures were used [40] ... 

Although typical catalyst preparation procedures vary slightly from one laboratory to another, the "conventional approach" is to deposit a metal salt on a support, convert this salt to the oxide, and then reduce to the metallic state. When two metals are simultaneously so treated and reduced, bimetallic clusters may form. However, it cannot be assumed that bimetallic clusters are produced since monometallic separate particles may predominate. In fact, it is perhaps the unusual case where bimetallics do form since there are many possible paths, both thermodynamic and kinetic, that can lead to (1) separate monometallic s, (2) one metal not reduced, (3) thermal segregation of bimetallic precursor particle, and/or (4) volatilization or migration of one metal. 

To stress the technical relevance of precipitated catalysts, Table 1 gives an overview of industrially used precipitated catalysts and supports. Since the catalyst compositions, and even less the catalysts preparation procedures for many industrial processes are not disclosed by the companies, this list is by no means comprehensive. 

Table 5 True and Apparent Sizes of Pd Particles Depending on the Textural and Microstructural Properties of the Support and Catalyst Preparation Procedure ... 

Surface Groups on Carbons and Catalyst Preparation Procedures... 

SURFACE GROUPS ON CARBONS AND CATALYST PREPARATION PROCEDURES... 

McHenry et al (12) reported at the 2nd Inti.Congress on Catalysis that Pt ions survived a severe reduction and were, according to the authors responsible for dehydrocyclization and aromatization. Some workers confirmed this claim (13-15). while some others rejected this conclusion (16-18). Because of the extreme importance of such conclusions for catalyst preparation procedures ("can and should the Pt ions be stabilized against the reduction ") we have addressed this question and we report below the results of our study. The questions to be answered are as follows. 

Co(OCOR)2/AlEt3/H20 initiates polymerization of 1,3-butadiene. Addition of phosphine ligands influences the structure and molecular weight of the polymer [75]. Sterically bulky phosphines decrease catalytic activity. Co(OCOR)2/MAO/f-BuCl is also effective for the polymerization of 1,3-buta-diene to produce the cis- 1,4-polymer [76]. The catalyst preparation procedure and aging time have a critical influence on the cis content and yield of the polymer. The reaction rate is reduced by addition of mesitylene or trimethoxybenzene to the reaction mixture [77]. The concentration of the active species of the catalyst is estimated based on the equilibrium between the Co and Al compounds in the reaction mixture [78]. 

The dissolution behaviour of the alumina support during the slurry phase impregnation steps of the catalyst preparation procedure was considered to be the cause of the high levels of cobalt-rich ultra fine particulates in secondary filtered wax. To prevent dissolution of the alumina support during the slurry phase impregnation step of the catalyst preparation procedure, a support modification procedure was developed to prevent acidic attack of the hydroxyl groups on the surface of the support. A modifier was chosen which had to conform to the following requirements ... 

The catalyst formulation is fixed by the composition and the properties of its washcoat components, by the amount of the various precious metals used, and by the catalyst preparation procedure. The composition and the properties of the washcoat are the key factors that govern the performance and the durabihty of the catalyst. 

As is shown in Figure 7, it was indicated that the temperature for 60% n-butane conversion was dependent on the surface area of (V0)2P207 irrespective of the catalyst preparation procedure more precisely, dependent on the surface area of (200) face (Figure 8). This indicates that (200) face is active and other faces are rather inactive. 

Pellets of CUAI2 alloy (53 wt. % Cu, 47 wt. % Al) and Cu-Al-Zn alloy (43.2 wt. % Cu, 39 wt. % Al, 17.8wt. % Zn), (3.8 mm x 5.4 mm dia), were leached in large excesses of two different leach solutions, 6.1 M sodium hydroxide and 0.62 M zincate in 6.1 M sodium hydroxide. Leaching was terminated by washing the pellets in distilled water to a pH of 7. The catalyst preparation procedure is described in greater detail elsewhere [7]. To simplify references to the four Raney catalysts Table 1 identifies them according to the precursor alloys and leach conditions used. 

Oxidation. Catalyst preparation procedures determine catalyst structures and consequent catalytic performance. The activity of combinations of oxides is often quite different from those of the individual oxides. For example, the capability of FejOj, the catalyst used to oxidize CH3OH to formaldehyde, to promote complete oxidation is nearly absent in iron(III) molybdate, Fe2(Mo04>3. ... 

The purpose of the present work has been to study the effect of various parameters that control the activity and selectivity patterns during the catalytic hydrogenation of cinnamaldehyde. The parameters studied are support type, active metal (or combination of metals) and catalyst preparation procedure. The last parameter has not been studied well, as is evident from the above literature survey. 

Fig. 1 Systematic approach for iterative optimization of catalyst preparation procedure and preparation-performance model.

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