Characteristics of the active sites on sulfated zirconia for n-butane isomerization

In situ spectroscopic investigation of activation, start-up and deactivation of promoted sulfated zirconia catalysts

“…The capacity of 2.0FeSZ to adsorb CO on Zr 4+ Lewis sites decreases with time on stream and the amount of adsorbed CO can thus not be taken as a measure for the catalytic activity of 2.0FeSZ in the present state. CO is a poison that inhibits isobutane formation as long as it is added to the feed [48,56]; instead of blocking active Lewis sites that are necessary for isomerization [48], it is reacting with the adsorbed carbenium ions [56,57], so that their transformation to isobutane is hindered. Our adsorption experiments show that Zr 4+ sites that are able to interact with CO are blocked during n-butane isomerization.…”

Olefin impurity effect on n-pentane bimolecular isomerization over WOx/ZrO2

“…Strong acid catalysts [1] such as chlorinated Pt/Al 2 O 3 [2][3][4] and heteropoly acids (HPAs) [5][6][7][8][9][10] have the ability to isomerize light alkanes such as n-butane (nC 4 ) and n-pentane (nC 5 ) and heavier ones such as n-hexane (nC 6 ) and n-heptane (nC 7 ) via a monomolecular reaction pathway. Sulfated zirconia (SZ) [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25], tungstated zirconia (WZ) [11] and various zeolites [4,6,[26][27][28][29][30] have been extensively investigated [25,[31][32][33][34][35][36], and unlike Pt/Al 2 O 3 and HPAs, they appear to isomerize lighter alkanes primarily through a bimolecular mechanism.…”

“…HPAs are very active but thermally unstable since they decompose at low temperatures (usually lower than 500°C), which makes their regeneration virtually impossible in industrial applications. SZ has been studied extensively [12][13][14][15][16][17][18][19][20]22,24,25,37,[39][40][41][42][43][44][45] for replacing current catalysts, especially for the isomerization of nC 4 . Even though more stable than Pt/Al 2 O 3 and HPAs, SZ catalysts suffer by severe deactivation due to coke deposition [22] and H 2 S in situ generation [44,46] in the presence of H 2 O [46,47].…”

An Integrated Catalytic and Transient Study of Sulfated Zirconias: Investigation of the Reaction Mechanism and the Role of Acidic Sites in n‐Butane Isomerization

“…[8,9] Previous studies in this field have employed a variety of characterization techniques and catalytic testing to describe the composition and the nature of the acidity, and their influence on the reaction mechanism, using different SZ model systems. [10][11][12][13][14][15][16][17] Changes in the surface structure of SZs were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), whereas adsorption of pyridine was used to determine Brønsted/Lewis ratios. [8,12,18] In situ investigations with nbutane under standard reaction conditions were performed using UV/Vis spectroscopy to study the formation of unsaturated compounds, [19] and temperature-programmed desorption (TPD) of ammonia was recently used to determine the number and distribution of acidic sites on SZ by a combination of IR spectroscopy, mass spectrometry, and a theoretical approach, whereby the cracking of n-heptane was correlated to strong Brønsted sites.…”