Desorption and Counterdiffusion Behavior of Benzene and Cumene in H-Mordenite

Abstract

The idealized mordenite pore structure comprises an array of parallel tubes only slightly greater in diameter than the minimum effective diameter of benzene and cumene molecules, and they cannot readily counterdiffuse in mordenite. The cumene desorptive diffusion coefficient from H-mordenite into benzene at 25°C decreased by over two orders of magnitude as the time of saturation before desorption was increased to 6 days. This decrease seems to be caused by the slow formation in the H-mordenite pores during the saturation step of radical ions and diisopropylbenzene molecules, the latter by the disproportionation of cumene. Both of these cause blockage of the pores. Most of the surface area of H-mordenite is apparently unavailable for reaction of aromatic species at temperatures moderately above ambient.

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

“…In some instances, the exterior surfaces of zeolites process reactants that are too big to adsorb completely 191 or diffuse too slowly [454][455][456] to fully permeate the adsorbate. Whether the exterior zeolite surface has a sufficiently regular structure to yield product distributions different from amorphous aluminosilicates continues to be a subject for debate.…”

Computer Simulations of Shape Selectivity Effects

“…either too large to adsorb completely [26] or diffuse too slowly [11][12][13] to fully permeate the adsorbate. Whether the exterior zeolite surface has a sufficiently regular structure to yield product distributions different from amorphous aluminosilicates remains a subject of debate.…”

“…Whether the exterior zeolite surface has a sufficiently regular structure to yield product distributions different from amorphous aluminosilicates remains a subject of debate. In reflecting the lack of agreement on the relevance of the exterior surface to shape selective catalysis, the process has been given a plethora of names, including pore mouth catalysis [11], key-lock mechanism [19,20], nesteffect [5,14], and exterior surface shape selectivity [14].…”

“…reactions on external surfaces and special effects'' [10]. Whereas progress has been made in establishing and understanding external surface reactions [11][12][13][14] (variously called ''nest effects'' [15] or ''pore mouth'' [10,11,[16][17][18] and ''key-lock'' [19][20][21][22] catalysis), the (other) ''special effects'' have mushroomed into a myriad of phenomena each with their individual name. An early example of these special effects is the ''window'' or ''cage effect'', coined by Chen et al [10,23].…”

The selectivity of -hexane hydroconversion on MOR-, MAZ-, and FAU-type zeolites

“…II. Partial adsorption catalysis: Zeolites preferentially process reactants at the exterior surface if they exhibit too high a Gibbs free energy of adsorption [42] or too high a Gibbs free energy barrier to adsorption [46][47][48] to fully penetrate the adsorbent. III.…”