Skeletal isomerization of linear butenes on tungsten promoted ferrierite Original Research Article

Samples of ammonium, protonic and potassium ferrierites were impregnated with tungsten species. The catalytic behavior of samples with and without tungsten during the linear butene isomerization reaction was studied. Tungsten loadings between 0.5 and 1.0% on ammonium ferrierite produce a synergetic effect both on activity and isobutene yield, while tungsten addition on the protonic form worsens the catalytic behavior of the unpromoted ferrierite. The presence of tungsten species on potassium ferrierite promotes the linear butene skeletal isomerization, with an optimum in the performance when the tungsten loading is between 3.5 and 4.0%. Tungsten species show a weak interaction with the potassium ferrierite surface. On the other hand, on protonic ferrierite the interaction is slightly stronger than on ammonium ferrierite, and the reduction of tungsten occurs practically in one step. The effect of both pretreatment and operational conditions over catalytic performance and deactivation of materials was also addressed. The higher the calcination temperature of ammonium ferrierite, the lower the linear butene conversion and the isobutene yield. Protonic ferrierite, tungsten promoted ammonium ferrierite, and tungsten promoted protonic ferrierite show similar qualitatively behaviors. After 5 min of reaction at any operational conditions, a high activity with low isobutene selectivity is observed. This behavior is related to the presence of strong acid sites. At long time-on-stream (TOS), the linear butene conversion at 450 °C is significantly higher than the one reached at 300 °C, while the isobutene yield remains between 12 and 18% for both reaction temperatures. Tungsten promoted potassium ferrierite samples display a different behavior. At 5 min the high activity is not reached, and both linear butene conversion and isobutene yield appear more stable with TOS; what is associated with the absence of strong acid sites. When reaction takes place at 450 °C, the isobutene yield significantly increases, approaching the yield obtained with the other samples. For all samples, the presence of hydrogen previously and during the reaction does not significantly modify the catalytic behavior, showing a small effect over the by-product distribution. By-products are formed from oligomers, which are among the products even at long TOS.