Differences in the morphology and vibrational dynamics of crystalline, glassy and amorphous silica – commercial implications

Parker, Stewart F.; Klehm, U.; Albers, Peter

doi:10.1039/d0ma00158a

Cited by 7 publications

(3 citation statements)

References 42 publications

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“…Hence, they would be expected to appear in the spectra. A comparison with the INS spectra of a variety of silicas , shows that the modes at 445, 535, 800, 1115, and 1205 cm –1 are all due to Si–O modes, the two high-energy modes are stretches and the remainder are deformations. The O–H stretching modes are observed by MAPS.…”

Section: Resultsmentioning

confidence: 99%

Counting the Acid Sites in a Commercial ZSM-5 Zeolite Catalyst

et al. 2022

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This work investigates the acid sites in a commercial ZSM-5 zeolite catalyst by a combination of spectroscopic and physical methods. The Brønsted acid sites in such catalysts are associated with the aluminum substituted into the zeolite lattice, which may not be identical to the total aluminum content of the zeolite. Inelastic neutron scattering spectroscopy (INS) directly quantifies the concentrations of Brønsted acid protons, silanol groups, and hydroxyl groups associated with extra-framework aluminum species. The INS measurements show that ∼50% of the total aluminum content of this particular zeolite is extra framework, a conclusion supported by solid-state NMR and ammonia temperature-programmed desorption (TPD) measurements. Evidence for the presence of extra-framework aluminum oxide species is also seen in neutron powder diffraction data from proton- and deuterium-exchanged samples. The differences between results from the different analytical methods are discussed, and the novelty of direct proton counting by INS in this typical commercial catalyst is emphasized.

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Section: Resultsmentioning

confidence: 99%

Counting the Acid Sites in a Commercial ZSM-5 Zeolite Catalyst

et al. 2022

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“…Furthermore, the very broad peak around 3000 cm –1 in the spectrum of NaLAS, which corresponds to the –OH stretching region, becomes much more intensive for the calcium salt. In parallel, a peak at 1653 cm –1 shows up, which belongs to the scissoring mode of water [ 61 , 62 ]. Consequently, the calcium salt is more strongly hydrated than NaLAS.…”

Section: Resultsmentioning

confidence: 99%

Binding of Ca2+ Ions to Alkylbenzene Sulfonates: Micelle Formation, Second Critical Concentration and Precipitation

et al. 2023

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Anionic surfactants, such as sodium linear alkylbenzene sulfonates (NaLAS), are utilized in various fields, including industry, household, and agriculture. The efficiency of their use in aqueous environments is significantly affected by the presence of cations, Ca2+ and Mg2+ in particular, as they can decrease the concentration of the surfactant due to precipitation. To understand cation–sulfonate interactions better, we study both NaLAS colloidal solutions in the presence of CaCl2 and precipitates forming at higher salt concentrations. Upon addition of CaCl2, we find the surface tension and critical micelle concentration of NaLAS to decrease significantly, in line with earlier findings for alkylbenzylsulfonates in the presence of divalent cations. Strikingly, an increase in the surface tension is discernible above 0.6 g L–1 NaLAS, accompanied by the decrease of apparent micelle sizes, which in turn gives rise to transparent systems. Thus, there appears to be a second critical concentration indicating another micellar equilibrium. Furthermore, the maximum salt tolerance of the surfactant is 0.1 g L–1 Ca2+, above which rapid precipitation occurs yielding sparingly soluble CaLAS2∙2H2O.

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“…While the scattering cross sections of Al, Si and O are only ∼10% that of 1 H (∼80 barn), there are more than ten times as many of them as there are hydrogen atoms. Comparison with the spectra of a variety of silicas, 50,51 shows that the weak modes at 445, 535, 800, 1115 and 1205 cm −1 are Si–O modes. The O–H stretching modes are observed by MAPS.…”

Section: Catalyst Characterisationmentioning

confidence: 97%