Cr-Ni bimetallic catalyst

Cr-Ni bimetallic catalyst-promoted redox addition of vinyl halides to aldehydes. 

We prepared Ni-M (M = Al, Cr, Cu, Co and Mo) catalysts supported on graphite, at low temperature, by coreduction of metal salt mixtures (NiXa, MX2) deposited on this support with sodium naphthalene as reducting agent. Quantitative microanalyses performed by STEM/EDX showed that the two metals were evenly distributed over graphite leaflets. The activity and the selectivity of these catalysts in the hydrogenation of citral to citronellal and citronellol have been compared with that of unsupported bimetallic catalysts, with the same atomic composition and prepared by the same procedure. It appeared that the nickel surface area of the supported catalysts was notably higher than that of the unsupported ones, but the support had almost no effect on the catalytic properties. 

Several reports indicate that Pt-based alloys are at least as good as pure Pt, and in many cases the alloyed material shows a better performance for the oxygen electroreduction (OER) [26, 27, 33, 46, 47, 48]. Experimental data on the catalytic activity of bimetallic surfaces regarding the OER is controversial. It is clear that certain bimetallic catalysts (Pt-Cr, Pt-Fe, Pt-Co, Pt-Ni) yield a slightly enhanced oxygen reduction current, but the reported degree of enhancement differs among researchers [2]. 

Figure 5. A x magnitudes for PtM (M = Fe, Cr, Ni, and Co) bimetallic catalysts and pure Pt in FI2S04 at 0.84 V prepared as described in Ref. 28. The region where the maximum is observed for OFi and O on Pt is indicated. Note the presence of the additional shoulder below 0 V when M atoms are on the surface (case for PtNi and PtCo), and the absence of these shoulders in the case of a Pt skin (case for PtFe and PtCr). Thus OH/Pt near a M island can be distinguished from OH/Pt distant from these islands.

Pt-alloys PtMe (Me = Cr, Mn, Co, Ni, V, Ti) were investigated early on, since they show an increased specific activity with respect to ORR [1, 2]. Enrichments and depletions of alloying metals on the particle interface were found, which influenced the electrochemical activity significantly. Predominant scientific success was achieved in the field of Pt-monolayer catalysts [3], the concept of Pt-skin electrocatalysts [4], and the concept of unalloyed Pt bimetallic catalysts [5]. 

The first published patent on LDHs as catalyst precursors used high supersaturation conditions. Mg/Al-COs, Ni/Al-CO3, Co/Mn/Al-C03, Co/Mn/Mg/Al - CO3, and Ni/Cr/Al - CO3 LDHs, as well as other bimetallic and multimetallic LDHs were synthesized by adding a solution containing the... 

It has been reported that the nature of support and the addition of promoters greatly affect the catalyst activity and stability. Previous studies [5] on Ni catalysts have shown that the addition of Cr results in the formation of bimetallic alloys, which are less susceptible to coke deposition. However, it was not possible to inhibit wholly the coke formation during reaction and consequently, the catalyst deactivation. Therefore, it is necessary, in these situations, to regenerate the catalyst and to re-establish the performance of catalysts. 

The metals that are more frequently found as components of Ziegler-Natta catalysts are some light elements of groups I-III of the periodic table (e.g., Li, Be, Mg, Al), present as organometaUic compounds and halides, or other derivatives of transition metals of groups IV-Vm (e.g., Ti, V, Cr, Mo, Rh, Rn, Co, and Ni). A typical example is the product(s) of the reaction between triethylaluminum and titanium tetrachloride. The composition of the product is not well defined but is believed to be either an alkylated metal halide (monometallic I) or a bimetallic complex involving a bridge between the two metals (II). 

The results obtained with bulk alloys can be also translated to more practical carbon supported PtM catalysts. In general, a certain increase in the mass activity (A/gpt) for the ORR reaction was found in PtM (M = Cr, V, Mn, Ni, Co) as compared to Pt/C. Again, it is difficult to extract accurate conclusions to explain the role of the foreign metal on the activity of carbon supported bimetallic (or polymetallic) electrocatalysts for the ORR since features such as particle size and size distribution, or metal loading cannot always be eliminated by normalization procedures. Paulus et studied... 

Sulfided bimetallic M-Mo/Al Oj catalysts (where M is Cr, Fe, Co, Ni, Ru, Rh, Pd, Re, Ir, or Pt) were studied for the selectivity of HDO of naphthalene to diphenylether compared to hydrogenation of naphthalene [93], CoMo shows high hydrogenation activity for C=C bonds, but it has only a relatively high selectivity ( / =1.90). Ru-Mo shows the highest selectivity for HDO but is only the third-most active metal combination (Fig. 9.12). Figure 9.12 depicts a volcano plot showing inoeased activity... 

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