Surface chemical states of aluminophosphate and silicoaluminophosphate molecular sieves

Abstract

Stark tuning effect as applied to the Pt-C-0 system. This suggests that the vibrational behavior of adsorbed CO or other IR-active molecules may provide a valuable probe of the electric field at the metal/ electrolyte interface. Future experiments should focus on determining the quantitative accuracy of this approach, by combining the IR measurements with more conventional electrochemical techniques for determining the PZC and the concentration of specifically adsorbed ions.

Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

“…Especially resonance 5 is interacting with different types of phosphorus species. Finally, the fact that Al(IV)/Al(VI) ratios decrease significantly after H 3 PO 4 introduction, indicate that TFAl species can also physically coordinate with phosphoric acid, adapting a reversible octahedral coordination, as has been suggested in the literature, where a 27 Al chemical shift and 31 P chemical shift at À10 ppm and À12 ppm were reported respectively. 14,59 This species is shown in Fig.…”

“…14 In order to check the reversibility of the phosphorus interaction, samples were washed with hot water. Table S5 (ESI †) shows that after washing 75% of the P is removed and it is apparent from 27 Al MAS NMR spectra and (c and d) FT-IR spectra, highlighting the OH-stretch region, and (e and f) 31 When ammonium hydrogen phosphate is used as a precursor, the absorption intensity of the SiOHAl band does not decrease as can be seen in Fig. 3d.…”

“…Fig. 6 (a and b) 27 Al MAS NMR, (c and d) FT-IR OH-stretch region spectra, and (e and f) 31 27 Al resonance 6 with 31 P resonance at À15 ppm and 27 Al resonances at 20 ppm to 25 ppm with 31 P resonance at À19 ppm. After washing two types of phosphorus with resonances at À24 ppm and À32 ppm interact with aluminium in resonance 3.…”

“…However, the Si-O-P bonds that are required for such a substitution have never been found in either phosphorus/H-ZSM-5 or SAPO materials and theoretical work has pointed to the unlikeliness of such bonds. 14,15,17,20,[29][30][31][32] Other possibilities of phosphorus-framework interaction have been suggested to arise from protonation of phosphoric acid by zeolitic bridging hydroxyl groups, stabilising the nearest neighbouring aluminium atom. 17 However, due to the low aluminium content generally found in H-ZSM-5, Al-O-Si-O-Al sites are quite rare and theoretical studies excluded the possibility of H 3 PO 4 protonation.…”

“…A set of samples, representing different steps in the phosphatation process, was prepared of which an overview is presented in Scheme S1 (ESI †). These samples have been studied using a multi-pronged spectroscopic approach, consisting of Fourier transform infrared spectroscopy (FT-IR), single pulse 27 Al, 31 P MAS NMR, 2D heteronuclear 27 Al-31 P correlation (HETCOR), 27 Al MQ MAS NMR spectroscopy, temperature programmed desorption (TPD) of pyridine, as monitored with FT-IR, and scanning transmission X-ray microscopy (STXM). Using this combination of characterization techniques we have elucidated many physicochemical phenomena, i.e.…”