Enhancement of the catalytic performance of H-clinoptilolite in propane–SCR–NOx process through controlled dealumination

Improved performance of HZSM-5 for the ethylbenzene/xylene isomerization reaction under industrial operating conditions

“…Physisorbed ammonia was egressed by consequent ow of a helium stream over the sample at 100 C. As a nal step, the sample was placed under a heating ramp of 10 C min À1 up to a temperature of 1000 C under a helium stream purge with a ow rate of 40 cm 3 min À1 . 27 Al isotope mass nuclear magnetic resonance ( 27 Al MAS NMR) spectra were obtained using a Bruker Avance III 400 WB instrument. Thermogravimetric analysis (TGA) was performed using a Diamond TG/DTG apparatus.…”

“…2,16 The same peak is present in the spectrum of the sample dealuminated with oxalic acid (DA1), although it is less pronounced. This attribution requires a complementary con-rming analysis, such as 27 Al NMR analysis, and will be discussed later in the text. A peak centered at about 3746.0 cm À1 is observed for the DA1 sample.…”

“…Ghasemian et al traced super acids due to oxo-aluminum species (due to extraframework aluminum) in dealuminated clinoptilolite zeolite from the high temperature NH 3 -TPD peaks observed at 700 C to 750 C. 27 However, the detailed work by Triantallidis et al on the dealumination of ZSM-5 zeolites with AHFS shows that this reagent produces samples free of extraframework aluminum. 11 Our 27 Al MAS NMR analysis also conrms this fact and will be discussed later. Accordingly, it may be stated that the 3657 cm À1 FTIR peak is related to strong bridging hydroxyls at Bronsted sites within the framework.…”

“…Fig. 7a and b illustrate the results of 27 Al MAS NMR analysis for the DA0, DA1, DA2 and DA3 samples. First of all, it should be stressed out that the original commercial H-ZSM-5 sample contains extraframework aluminum of octahedral character.…”

“…4 Detailed studies by Mueller et al investigated the effects of ZSM-5 dealumination using different concentrations of oxalic acid and zeolites with different initial Si/Al molar ratios from 9 to 46. 5 They monitored the dealumination process by 27 Al, 29 Si and 1 H MAS NMR together with nitrogen adsorption/ desorption analysis. While they succeeded in dealuminating the different parent zeolites by this method, the catalytic behavior of the product samples was not studied.…”