Phosphorus oxide, properties

Vanadium phosphorus oxides (VPO) are commercially used as catalysts for the s5mthesis of maleic anhydride from the partial oxidation of n-butane. The phase constitution and the morphology of the catalyst are found to be dependent on the preparation routes and the applied solvent [78]. Recently, a method to prepare VPO catalysts in aqueous solution at elevated temperature was reported [79]. In addition to the linear relationship between specific activity and surface area, a small group of catalysts exhibit enhanced activity, which could be due to the combination of a higher proportion of V phases in the bulk of vanadyl pyrophosphate (V0)2P207 catalyst [79, 80]. With high relevance to the catalytic properties, the microstructure characterisation of VPO therefore is of great importance. 

Several readily-oxidized nonmetallic elements have found widespread use in the field of pyrotechnics. The requirements again are stability to air and moisture, good heat-per-gram output, and reasonable cost. Materials in common use include sulfur, boron, silicon, and phosphorus. Their properties are summarized in Table 3.5. 

In our previous studies of butane oxidation over silica-supported vanadium-phosphorus oxide (VPO) catalysts, it was observed that the selectivity for maleic anhydride increased with the PA ratio, from about 25% for catalysts with a PA ratio of unity to about 50% for a PA7 ratio of about two [2,3]. In order to more fully understand the properties of VPO catalysts with P/V ratios near 2, we have prepared and characterized silica-supported and unsupported catalysts derived from V0(H2P04)2, the precursor to VOfPOjjj, and studied the selective oxidation of a series of alkanes ranging from CjHg to CjHij over the bulk catalyst. 

The similar structural and catalytic properties of the SiOj-supported and unsupported samples prepared from the same precursor suggest that the same active surface is formed on both types of samples. The higher conversions obtained with the supported samples could be attributed to higher dispersions of the VPO compounds. The slightly lower maleic anhydride selectivity observed for catalyst A than B or the bulk catalyst could be due to some phosphorus atoms interacting with the silica surface rather than with vanadium atoms, such that the P/V ratio is less than two in the VPO compounds. Addition of phosphorus to catalyst B replenished this lost phosphorus. Previous studies of supported vanadium-phosphorus oxides have shown that some phosphorus atoms can be associated with the silica [2,8]. The catalytic properties of the supported samples as well as the LRS are similar to the SiOj-supported PA =2 VPO samples prepared previously [2,3]. These earlier samples were prepared by adding H3PO4 to PA =1 samples synthesized by various synthesis routes. Thus, for the supported samples, the method of preparation is much less important than the composition. 

The detection of the periodic system of chemical elements was a break through in the theoretical understanding of chemistry. Hefferlin discusses periodicities of chemical elements and small molecules. He shows how general the concept of posets is. Why not explore the properties of small molecules by means of a Hasse diagram Hefferlin shows by the example of Phosphorus oxides how this may be done. 

The catalyst should function as an electron acceptor or have acidic properties. It should also have a low porosity so that total oxidation of the maleic anhydride is prevented by mass transfer resistance. Vanadium phosphorus oxide complexes in which several V oxidation states are combined are used mean specific surface area... 

Definition Starch crosslinked with sodium trimetaphosphate or phosphorus oxychloride and etherified with propylene oxide Properties Wh. or nearly wh. powd. or gran. flakes, amorphous powd., or coarse particles if pregelatinized... 

Stackman [29] carried out a study to find systems suitable for reducing the flammability of polyethylene terephthalate (PET) and poly-1,4-butylene terephthalate (PBT) while retaining the chemical and physical properties of the original polymers. The additives used were phosphine oxides, phosphonates and phosphates and their activity was assessed by means of an oxygen index test. Most of the phosphorus esters were found to be volatile under the blending conditions and both the halogenated phosphorus esters and halogenated derivatives of phosphorus oxide proved to be ineffective as flame retardants. 

The most important property of phosphorus(V) oxide is its great tendency to react with water, either free or combined. It reacts with ordinary water with great vigour, and much heat is evolved trioxo-phosphoric(V) acid is formed, but the local heating may convert some of this to tetraoxophosphoric(V) acid ... 

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