No abstract

No abstract

No abstract

No abstract

No abstract

No abstract

-pinene isomerization reaction was studied on catalysts based on H3PW12O40 (HPW) supported on TiO2, SiO2 and ZrO2nH2O. Catalysts with a 40% nominal charge of phosphotungstic acid (HPW) were prepared by impregnation of supports with a HPW solution. The study of the isomerization reaction was carried out in liquid phase by using a discontinuous reactor, magnetically stirred and maintaining a constant temperature. The catalyst supported on SiO2 resulted to be the most active while the one supported on ZrO2nH2O was the less active. This behavior correlated with the number and strength of the acid sites. XRD studies revealed the formation of HPW crystals when it was supported on SiO2.]]>

Transformations of α-pinene, limonene, terpinolene, and α-terpinene were studied in liquid phase on sulfated zirconia having 15% H 2 SO 4 , with the aim of identifing the pathway of α-pinene isomerization. The principal products obtained in α-pinene isomerization were camphene, tricyclene, limonene, and terpinolene; the concentration maxima observed at 120°C and 180 min were 53, 6.1, 7.7, and 3.0%, respectively. The principal products formed in the limonene transformation after a 20-min reaction time were terpinolene, α-terpinene, and γ-terpinene; then the concentration of these products decreased. The terpinolene reaction yielded principally m-cymenene, whereas the α-terpinene transformation produced p-cymene. Studies of the initial rates of transformation of terpenes indicate a very high rate for α-pinene, intermediate for limonene and α-terpinene, and very low for terpinolene. The scheme proposed to interpret the results of the α-pinene isomerization reaction on sulfated zirconia is in agreement with reaction schemes proposed by A. Allahverdiev, S. Irandoust, and D.Y. Murzin (Isomerization of α-Pinene over Clinoptilolite, Camphene is an important intermediate in the chemical industry; the main use is in camphor synthesis. Camphene is obtained as the principal reaction product when α-pinene isomerization is performed in a liquid phase in the presence of acid catalysts, as well as limonene, tricyclene, terpinolene, and other mono-and bicyclic compounds.The commercial process for camphene production uses TiO 2 catalysts treated with acids, but the reaction rate on these catalysts is slow, and more active catalysts are desirable. Zeolites, clays, and different oxides have been used with this purpose (1-8). Our group reported previously the isomerization of α-pinene on sulfated zirconia with and without modifications by Fe and Mn, zirconia with molybdenum and tungsten, and kaolinitic and bentonitic clays (9,10).The activity is associated with the catalyst acidity and the type of active sites, and the strength of the latter has an effect on the ratio of selectivities in bicyclic to monocyclic products.Severino et al.(1) maintain that Lewis sites favor the formation of bi-and tricyclic products whereas Brönsted sites favor the formation of monocyclic products.Ion-exchanged natural zeolites give two main groups of products: bicyclic and monocyclic. Camphene and bicyclic products are preferentially formed on Lewis sites from α-pinene, and monocyclic products are formed on Brönsted sites (2).Reaction pathways using clays, zeolites, and resins for the isomerization of α-pinene are found in the literature (3-6). These mechanisms were deduced from experimental results of the α-pinene isomerization reaction.Zirconium oxide, when modified with sulfate anion, forms a highly acidic or superacidic catalyst that exhibits superior catalytic activity for the catalysis of isomerization reactions. Catalysts of sulfated zirconia are active in α-pinene isomerization (7,9); in the present work, sulfated zirconia (15%) was selected to s...