Raymond J. Gorte

Department of Chemical Engineering

University of Pennsylvania

Philadelphia, PA 19104

Zeolites and other solid acids have great potential for replacing homogeneous acids in a wide range of catalytic applications. However, our understanding of the nature of acidity in solids and our ability to define that acidity in a quantitative manner is still not even close to providing us with the ability to choose a particular material or set of reaction conditions for all but a few reactions. Reaction mechanisms on solid acids are likely to be similar to mechanisms in solution phase; but it is easily shown that methods used to describe acidity in homogeneous acids, such as pK_a, are not useful in solid acids. This talk will describe some of the work in our laboratory which is aimed at developing the capability to define and characterize acidity in a quantitative manner and predict reaction pathways for a wide range of reactions. Methods used for characterization include temperature-programmed desorption, ¹³C NMR, and microcalorimetry.

The overall goal in our work is to understand reaction chemistry in zeolites well enough to be able to carry out reactions which currently require solution-phase acids. The primary techniques will involve microcalorimetry and TPD-TGA measurements, as well as reactor studies. Since most of our equipment is home-built and relatively inexpensive, I would propose that students spend time working in my laboratory for at least one year, then return to SA to continue working on the project. I will provide equipment designs.

1) Alkylation reactions on zeolites. An interesting reaction is the alkylation of benzene with acetic acid. Recent work has shown that this cannot be carried out in a zeolite because acetic acid interacts too strongly with the acid sites (The acid is a base!). Understanding that the zeolite is not like a solution phase acid may allow us to develop methodologies that may lead to interesting new ways to do this reaction (and others like it) on a heterogeneous acid.

2) We have recently developed the ability to carry out microcalorimetry measurements at 195 K. ("A Calorimetric Investigation of CO and N₂ for Characterization of Acidity in H-MFI", S. Savitz, A.L. Myers, and R.J. Gorte, Journal of Physical Chemistry B, 103 (1999) 3687.) This capability opens many doors for novel types of study. For example, we now have the ability to probe alkali ions by looking at the adsorption of CO quantitatively. Materials like Li-LSX can be examined in order to determine the nature of ion-molecule interactions in separations. Also, since heats of adsorption change with pore diameter, the low-temperature calorimetric measurements may be useful to directly measure pore-size distributions in microporous materials.

3) A particularly intriguing material is H-[Fe]MFI, the Fe substituted zeolite. Recent work at Zeolyst/PQ suggests that materials of this type can be produced which have stabilities similar to that of normal Al-containing zeolites. What makes these materials intriguing is that they are catalytic for many interesting reactions, but they are not very active for the oligomerization and cracking of olefins. This is VERY important. Most reactions involving zeolites are difficult to perform on zeolites because of the high rate of oligomerization. The fact that this does not occur readily on the acid sites formed by Fe opens up a number of interesting possibilities for selective chemistry.