Increased Sulfur Tolerance of Pt/KL Catalysts Prepared by Vapor-Phase Impregnation and Containing a Tm Promoter

n-Octane aromatization on Pt-containing non-acidic large pore zeolite catalysts

“…As reported previously [20,26], the adsorption of CO on small Pt clusters inside the L-zeolite channels leads to the formation of Pt carbonyls, which result from a disruption of the Pt clusters by interaction with CO. These Pt carbonyls are stabilized inside Lzeolite channels and exhibit characteristic IR adsorption bands below 2000 cm )1 .…”

“…It is important to qualify this term because in many studies comparisons have been made with Pt/K-LTL catalysts in which a large fraction of the Pt particles were located outside the zeolite channels, as we have previously discussed [26]. By using a variety of characterization techniques, we have demonstrated in several publications that the vapor phase impregnation (VPI) method that we employ results in the majority of the Pt clusters inside the zeolite structure [17,[19][20][21]. Interestingly, although the well-prepared Pt/ K-LTL catalysts exhibited a very high selectivity in the aromatization of n-hexane, it did not result in high selectivity to C8-aromatics [26].…”

“…Many studies have been conducted to understand the uniqueness of this catalyst and its ability to aromatize n-hexane [7][8][9][10][11][12][13][14] as well as to improve its tolerance to sulfur, which is a weakness of this unique material [15][16][17][18][19][20][21][22]. A well-recognized fact is that the KL zeolite structure is able to stabilize extremely small Pt clusters (<1 nm) in a completely non-acidic environment, two conditions that are needed in the selective aromatization pathway [23].…”

Heterogeneous Catalyst Deactivation and Regeneration: A Review

“…For example, Pt-containing naphtha reforming catalysts are often pre-sulfided to minimize unwanted cracking reactions. On basic Pt/KL zeolite catalysts, these short term, low concentration exposures are beneficial to produce Pt ensemble sizes that promote aromatization, while longer term or higher concentration exposures poison the catalyst both by forming Pt-S bonds and producing large crystallites that block pores, as shown by transmission electron microscopy (TEM) and X-ray absorption fine structure spectroscopy (EXAFS), and favor only dehydrogenation [50][51][52][53]. Other examples are sulfur added to Fischer-Tropsch catalysts that have been reported to have either beneficial or negligibly harmful effects, which are important considerations in setting the minimum gas clean-up requirements [27,30,[54][55][56].…”

“…These species, including rare earth oxides of thulium (Tm) [50] or Ce [51] and simple zinc oxide, essentially act as sacrificial stoichiometric reactants to protect the active metal by preferentially adsorbing the poison. These traps can extend the catalyst life, but because they are not catalytic as they perform, they are necessarily temporary agents if the poison remains in the feed to the process.…”