Nickel catalysts phosphate supports

The interaction between oxidic nickel or cobalt and the phosphated support becomes weaker (114,115). Less nickel or cobalt is lost to the support, and more is available for the formation of the active Ni-Mo-S phase on the catalyst surface. 

As an attempt in this direction, a hierarchy was recently developed for nickel catalysts (6). The basic idea is to monitor the chemical properties of a catalyst as probed by hydrogen chemisorption, ethane hydrogenolysis, and carbon monoxide hydrogenation. The hierarchy, originally developed for Ni/I O catalysts, was later extended to nickel supported on phosphate-containing materials and a niobia-silica surface phase oxide. In this paper the usefulness of the hierarchy will be illustrated by its ability to differentiate between support effects of niobia and phosphate, and to establish the intermediate degree of interaction of niboia-silica. 

Ethane Hydrogenolysis. Table II summarizes the kinetic results of ethane hydrogenolysis over nickel catalysts on phosphate (15), niobia (6 ), and niobia-silica (9) supports. As a point of jjefer ... 

Carbon Monoxide Hydrogenation. The activities of these nickel catalysts in CO hydrogenation are shown in Table III. The phosphate-supported catalysts as a group are about a factor of 5 to 10... 

Although palladium occupies the dominant position in semi-hydrogenation catalysts, it is by no means the only metal suitable for formulation into a viable catalyst. Mention has already been made of the nickel boride alternatives, with or without copper promotion, for example. Other examples include the skeletal catalyst Raney nickel [69], alumina-supported nickel [70], and aluminum phosphate-supported nickel [71] (Eqs 21 and 22) ... 

Resorcinol Derivatives. Aminophenols (qv) are important intermediates for the syntheses of dyes or active molecules for agrochemistry and pharmacy. Syntheses have been described involving resorcinol reacting with amines (91). For these reactions, a number of catalysts have been used / -toluene sulfonic acid (92), zinc chloride (93), zeoHtes and clays (94), and oxides supported on siUca (95). In particular, catalysts performing the condensation of ammonia with resorcinol have been described gadolinium oxide on siUca (96), nickel, or zinc phosphates (97), and iron phosphate (98). 

This paper describes the catalytic activity of nickel phosphide supported on silica, alumina, and carbon-coated alumina in the hydrodesulfurization of 4,6-dimethyldibenzothiophene. The catalysts are made by the reduction of phosphate precursors. On the silica support the phosphate is reduced easily to form nickel phosphide with hi catalytic activity, but on the alumina support interactions between the phosphate and the alumina hinder the reduction. The addition of a carbon overlayer on alumina decreases the interactions and leads to the formation of an active phosphide phase. 

It is thus likely that the carbon coating on the alumina support lessened the interaction between AI2O3 and P and inhibited the formation of nickel phosphate after calcination and also lowered the reduction temperature. Structural models of the supported Ni2P catalysts are shown in Figure 4. 

This article is focused on HDN, the removal of nitrogen from compounds in oil fractions. Hydrodemetallization, the removal of nickel and vanadium, is not discussed, and HDS is discussed only as it is relevant to HDN. Section II is a discussion of HDN on sulfidic catalysts the emphasis is on the mechanisms of HDN and how nitrogen can be removed from specific molecules with the aid of sulfidic catalysts. Before the discussion of these mechanisms, Section II.A provides a brief description of the synthesis of the catalyst from the oxidic to the sulfidic form, followed by current ideas about the structure of the final, sulfidic catalyst and the catalytic sites. All this information is presented with the aim of improving our understanding of the catalytic mechanisms. Section II.B includes a discussion of HDN mechanisms on sulfidic catalysts to explain the reactions that take place in today s industrial HDN processes. Section II.C is a review of the role of phosphate and fluorine additives and current thinking about how they improve catalytic activity. Section II.D presents other possibilities for increasing the activity of the catalyst, such as by means of other transition-metal sulfides and the use of supports other than alumina. 

A mixture of formalin and ethanol was passed at 240—320 C over various metal oxides supported on silica gel and metal phosphates. The main products were acrolein, acetaldehyde, methanol, and carbon dioxide. Acidic catalysts such as V-P oxides promoted the dehydration of ethanol to ethene. The best catalytic performances for acrolein formation are obtained with nickel phosphate and silica-supported tungsten, zinc, nickel, and magnesium oxides. With a catalyst with a P/Ni atomic ratio of 2/3, the yields of acrolein reach 52 and 65 mol% on ethanol basis with HCHO/ethanol molar ratios of 2 and 3, respectively. Acetaldehyde and methanol are formed by a hydrogen transfer reaction from ethanol to formaldehyde. Then acrolein is formed by an aldol condensation of formaldehyde with the produced acetaldehyde [40],... 

---