Samarium phosphate

The influence of temperature on the selectivity was examined systematically. This study had not drown an interesting catalytic activity for catalyst which are weakly active at 270°C but had shown some important variation in selectivity for the more active catalysts boron, lanthanum, cerium III, samarium phosphate and niobium oxyphosphate. Catalytic results for those catalysts as a function of the temperature are reported in Table 2 and selectivity in O-alkylated products is simplified on Figure 3. 

The influence of catalyst calcination temperature was studied in the case of samarium phosphate as those products show a thermal phase transition between 600 and 700°C (ref. 10). Catalytic results are summarized in Table 3. 

Table 3. Influence of samarium phosphate calcination temperature on selectivity in O-methylation of catechol...

Samarium phosphate calcinated at 700°C and then of monoclinical structure, shows a very promissing activity and selectivity in O-alkylated products even at high conversion of catechol. 

CATALYSIS BY RARE EARTH PHOSPHATE HI. CHARACTERISATION OF SAMARIUM PHOSPHATE AND SAMARIUM PHOSPHATE-CESIUM HYDROGENOPHOSPHATE AS KEY CATALYSTS FOR O-ALKYLATION OF PHENOLS... 

Samarium phosphates, impregnated or not by cesium hydrogenophosphate, selective catalysts for O-alkylation of phenols, have been characterised by various techniques. This study has shown that ... 

Samarium phosphate has an intrinsic acidic activity which can only be observed on products calcinated at a temperature of 700°C and which therefore possess a monoclinic structure. 

Samarium phosphate calcinated at lower temperatures, with an hexagonal structure has acido-basic characteristics highly dependant on the synthetic route use ... 

Particularly, a synergism between cesium hydrogenophosphate and samarium phosphate has been observed for the O-alkylation of dihydroxy-benzene (ref. 2). We described in this paper some characterizations of this solid doped or not, that may allow to explain catalytic results. 

Samarium phosphate was prepared by wet synthesis starting from samarium carbonate (Sm2(C03)3, originated RP). Precipitation of phosphate by phosphoric acid is conducted at 80°C by addition of a samarium carbonate suspension in a vessel containing phosphoric acid. After the end of the addition, the solid could be treated by ammonia at pH = 9. Cesium hydrogenophosphate is introduced by wetness impregnation of the dried (110°C) solid. 

We have compared the specific surface area thermal evolution of samarium phosphate just dried or samarium phosphate impregnated by cesium hydrogeno-... 

Samarium phosphate precipitates as an hexagonal phase and shows a phase transition between 600 and 700°C to form a more closed monoclinic phase. Those results are in good agreement with schneider s published datas (ref. 4) reviewing crystalline structure studies about rare earth orthophosphates. 

We have reported in Table 5, methylbutynol conversion at the 12th pulse and the acidic (A), basic activities (B) and activity due to acid base pairs (B) obtained for each samarium phosphate. The evolution of acido properties conversion of MBOH and selectivity in the various products formed as a function of preparation methods and calcination temperatures are reported Figures 7 and 8. 

Table 5. Acidobasicity of samarium phosphate determined by reaction of MBOH...

If we compare products calcinated at 500°C, SmP04 without treatment has a totally acidic behaviour while the sample treated at pH = 9 as a totally basic behaviour. The basic behaviour observed for SmP04 treated at pH = 9 indicates the presence of residual anions coming from the ammoniacal neutralization step. When calcinated at 700 °C, both products present comparable behaviour with an higher acidity for the phosphate not treated. At 700°C, we find the intrinsic acidic activity of samarium phosphate. 

A activity = mmol MBOH transformed per surface unit and per hour Fig. 7. Acido-basic properties of samarium phosphate... 

Cesium salt added by wetness impregnation (10 % w/w) has a sintering effect on the calcination of samarium phosphate. The examination of structural and textural data shows that the cesium does not enter the crystalline network. The cesium salt is uniformly distributed on crystallites surface and the special morphology of samarium phosphate makes the cesium retained in the porosity of the solid. 

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