Selective Alkylation of Benzene with Propane over Bifunctional Pt-Heteropoly Acid Catalyst

Abstract

The alkylation of benzene with propane to yield isopropylbenzene proceeds with high selectivity over bifunctional metal-acid catalysts comprising Pt and Keggin heteropoly acid in a fixed-bed reactor at 250-350 o C and 1 bar pressure. Most efficiently the reaction occurs over Pt/H 4 SiW 12 O 40 /SiO 2 catalyst at 300 o C, giving isopropylbenzene with 90-93% selectivity at 6-8% benzene conversion, significantly exceeding the efficiency of previously reported Pt/HZSM-5 catalyst. The alkylation proceeds through bifunctional reaction pathway including dehydrogenation of propane to propene (1) on Pt sites followed by benzene alkylation with propene (2) on acid sites. At Pt loadings above 0.5%, step (1) is at fast quasi-equilibrium, and step (2) is the rate-limiting one.

Selective Alkylation of Benzene by Propane over Bifunctional Pd-Acid Catalysts

“…Also, we looked at the effect of gold additives on catalyst performance by testing the corresponding AuPd-HSiW and AuPd-HZSM-5 bimetallic catalysts. It is demonstrated that in benzene alkylation with propane, the Pd-HSiW and Pd-HZSM-5 catalysts perform similarly to their Pt counterparts, Pt-HSiW and Pt-HZSM-5, as reported previously [18]. The addition of gold to Pd-HSiW is shown to enhance the activity of this catalyst, although the Au-HSiW without Pd is inert.…”

“…It is essential to compare the bifunctional Pd catalysts under study with previously reported Pt catalysts [18] under the same reaction conditions. Therefore, the Pd catalysts were tested in benzene alkylation with propane in the same system at 300 • C, contact time W/F = 80 g h mol −1 and [C 6 H 6 ]/[C 3 H 8 ] = 1:9 mol/mol without dilution of the gas feed with an inert gas, as described previously [18].…”

“…The alkylation of benzene with ethene and propene is used to manufacture ethylbenzene (EtPh) and isopropylbenzene (iPrPh), which are the intermediates in styrene and phenol production, respectively [1]. It has been demonstrated that ethene and propene can be replaced by abundant and inexpensive alkanes, ethane and propane, which would lead to the more cost-effective and environmentally friendly production of these commodity chemicals [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The alkylation of benzene with light alkanes occurs in the gas phase in the presence of solid bifunctional metal-acid catalysts, which operate via a pathway, shown in Scheme 1, including the dehydrogenation of alkane on metal sites to form alkene and H 2 (step 1) followed by the alkylation of benzene with the alkene on acid sites (step 2).…”

“…The main product was nPrPh (50% selectivity) rather than iPrPh [13], which would be the favourable product from the carbenium ion mechanism. This may be due to the shape selectivity control imposed by the zeolite microporous environment [18]. A much more selective alkylation of benzene by propane (90-93% iPrPh selectivity) has been reported using a mesoporous silica-supported Pt-heteropoly acid catalyst, Pt/H 4 SiW 12 O 40 /SiO 2 , based on the Keggin-type 12-tungstosilicic acid H 4 SiW 12 O 40 (HSiW) [18].…”

“…A much more selective alkylation of benzene by propane (90-93% iPrPh selectivity) has been reported using a mesoporous silica-supported Pt-heteropoly acid catalyst, Pt/H 4 SiW 12 O 40 /SiO 2 , based on the Keggin-type 12-tungstosilicic acid H 4 SiW 12 O 40 (HSiW) [18]. Notably, HSiW is superior to its stronger analogue H 3 PW 12 O 40 in this reaction, probably due to its larger number of proton sites and better resistance to coking [18].…”