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In an effort to understand the effects of H2O activity on zeolite formation, we have synthesized LTA zeolite using a combination of freezing processes and varying drying temperatures. Sodium aluminate and sodium silicate were used to form LTA zeolite, according to the IZA (International Zeolite Association) protocol. The synthesis steps were modified by adding the precursor frozen process by a rapid liquid nitrogen (−196 °C) treatment or slow conventional freezer treatment (−20 °C). The samples were subsequently sonicated and then dried at 80 °C or 40 °C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed on the samples immediately after the drying process as well as after 2 weeks and 1 month of aging the solid products. The results indicated that LTA zeolite does not form. The silica-alumina precursor after both freezing processes and after being dried at 80 °C showed the presence of sodalite displaying stable behavior over time. Both sets of samples dried at 40 °C and did not show the presence of zeolite immediately after the drying process. However, after 2 weeks, the liquid nitrogen–frozen precursor was characterized by the presence of EMT whereas zeolites never formed in the −20 °C samples. These results suggest that freezing processes differently control the H2O activity during the drying and aging processes in the solid state. Thus, although the precursor chemical composition is the same, the type of zeolite formed is different.

In an effort to understand the effects of H2O activity on zeolite formation, we have synthesized LTA zeolite using a combination of freezing processes and varying drying temperatures. Sodium aluminate and sodium silicate were used to form LTA zeolite, according to the IZA (International Zeolite Association) protocol. The synthesis steps were modified by adding the precursor frozen process by a rapid liquid nitrogen (&minus, 196 &deg, C) treatment or slow conventional freezer treatment (&minus, 20 &deg, C). The samples were subsequently sonicated and then dried at 80 &deg, C or 40 &deg, C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed on the samples immediately after the drying process as well as after 2 weeks and 1 month of aging the solid products. The results indicated that LTA zeolite does not form. The silica-alumina precursor after both freezing processes and after being dried at 80 &deg, C showed the presence of sodalite displaying stable behavior over time. Both sets of samples dried at 40 &deg, C and did not show the presence of zeolite immediately after the drying process. However, after 2 weeks, the liquid nitrogen&ndash, frozen precursor was characterized by the presence of EMT whereas zeolites never formed in the &minus, C samples. These results suggest that freezing processes differently control the H2O activity during the drying and aging processes in the solid state. Thus, although the precursor chemical composition is the same, the type of zeolite formed is different.

Ion scattering using ultralow energy projectiles is considered to be a unique method to probe the nature of molecular surfaces because of its capacity to probe the very top, atomically thin layers. Here, we examine one of the most studied molecular solids, water-ice, using this technique. When ice surface undergoes the amorphous to crystalline transition, an ultralow energy reactive projectile identifies the change through the reaction product formed. It is shown that ultralow energy (2, 3, 4, 5, 6, and 7 eV) CH2 + (or CD2 +) collision on amorphous D2O (or H 2O) ice makes CHD+, while crystalline ice does not. The projectile undergoes H/D exchange with the dangling -OD (-OH) bond present on amorphous ice surfaces. It is also shown that H/D exchange product disappears when amorphous ice is annealed to the crystalline phase. The H/D exchange reaction is shown to be sensitive only to the surface layers of ice as it disappears when the surface is covered with long chain alcohols like 1-pentanol as the ice surfaces become inaccessible for the incoming projectile. This article shows that ultralow energy reactive ion collision is a novel method to distinguish phase transitions in molecular solids. � 2013 American Chemical Society.

The first principles approaches, density functional theory (DFT) and quantum Monte Carlo, have been used to examine the balance between van der Waals (vdW) forces and hydrogen (H) bonding in ambient and high pressure phases of ice. At higher pressure, the contribution to the lattice energy from vdW increases and that from H bonding decreases, leading vdW to have a substantial effect on the transition pressures between the crystalline ice phases. An important consequence, likely to be of relevance to molecular crystals in general, is that transition pressures obtained from DFT functionals which neglect vdW forces are greatly overestimated., Submitted to Phys. Rev. Lett., 5 pages, 3 figures

The molecular ion of dihydrogen (H 2 +) is produced by 1 eV collisions of protons (H +) on amorphous water ice surfaces. The reaction is also observed on crystalline ice surfaces, but with lower efficiency. Collisions of D + on amorphous H 2O and D 2O ices yield D 2 + on the former, subsequent to isotope exchange on the H 2O surface. Ultra-low-energy collision-induced dihydrogen ion production is also observed from alkanol surfaces, with decreasing efficiency as the alkyl chain length increases. There is no corresponding reaction on solid hexane. This endothermic reaction, with implications for interstellar chemistry and plasma etching processes, is proposed to occur as a result of stabilization of the other reaction product, a hydroxyl radical (OH �), on water surfaces through hydrogen-bonding interactions with the surface. These results point to an interesting chemistry involving ultra-low-energy ions on molecular solids. � 2011 American Chemical Society.

Membres du Jury: Aycard JP; Chiavassa T; Girardet C; d'Hendecourt L; Hynes JT; Kister J; Mascetti J; Adsorption of ozone and cyanoacetylene on amorphous water ice was characterized by FTIR spectrometry between 10 and 180 K. Ozone is adsorbed on dangling OH of the ice surface and a desorption activation energy of 20 kJ/mol was measured by Temperature Programmed Desorption (TPD) coupled with FTIR. This value was confirmed by periodical ab initio calculations. Ozone forms a hydrogen bond with the ice surface. Previously to these periodical calculations, the O3•••H2O complexes were modelized. Cyanoacetylene shows two adsorption states on amorphous ice. The first, between 15 and 45 K, is characterized by a hydrogen bond between dangling OH and nitrogen atom of cyanoacetylene. The second, between 45 and 110 K, implies a hydrogen bond between a dangling O of the ice surface and a hydrogen atom of cyanoacetylene. The activation desorption energy for the second state, measured by TPD, is equal to 39 kJ/mol. A proton donor or acceptor character of the cyanoacetylene with ice was observed. These effects also appear in isolated cyanoacetylene∙∙∙water complexes observed in cryogenic matrix. The relative stabilities were determined from ab initio calculations. The kinetic or thermodynamic nature of the adsorption processes was discussed. A preliminary photochemical study of ozone co-adsorbed on ice surface with cyanoacetylene shows that a reaction occurs. This reaction leads to the formation of H2O2, O2 and a third product supposed to be a ketene.; L'adsorption de l'ozone et du cyanoacétylène sur une surface de glace amorphe d'eau a été caractérisée par spectrométrie IRTF entre 10 et 180K. L'ozone s'adsorbe sur les OH libres de surface de la glace et une énergie d'activation de désorption de 20 kJ/mol a été mesurée par Désorption Programmée en Température (DPT) couplée à l'IRTF. Cette valeur a été confirmée par des calculs quantiques ab initio de type périodique et l'interaction a été caractérisée comme étant de type liaison hydrogène. En préliminaire au calcul périodique, les complexes O3•••H2O ont également été modélisés. Le cyanoacétylène montre deux états d'adsorption sur la surface de glace amorphe, le premier, entre 15 et 45 K, se caractérise par l'existence d'une liaison hydrogène entre les OH libres de surface de la glace et l'atome d'azote du cyanoacétylène, le second entre 45 et 110 K, met aussi en jeu une liaison hydrogène entre un doublet libre d'un atome d'oxygène de surface de la glace et l'atome d'hydrogène du cyanoacétylène. L'énergie d'activation de désorption pour le deuxième état, déterminée par DPT, est égale à 39 kJ/mol. Un caractère donneur et accepteur de proton du cyanoacétylène vis à vis de la glace est observé. Ces effets apparaîssent aussi lors de l'étude des complexes cyanoacétylène•••eau en matrice d'argon. Les stabilités relatives ont été déterminées par calcul ab initio. La nature cinétique et thermodynamique des processus d'adsorption est discutée. Une étude préliminaire de la photochimie de l'ozone co-adsorbé sur de la glace amorphe avec du cyanoacétylène a montré la formation de H2O2, de O2 et d'un troisième produit de réaction qui pourrait être un cétène.

Adsorption of ozone and cyanoacetylene on amorphous water ice was characterized by FTIR spectrometry between 10 and 180 K. Ozone is adsorbed on dangling OH of the ice surface and a desorption activation energy of 20 kJ/mol was measured by Temperature Programmed Desorption (TPD) coupled with FTIR. This value was confirmed by periodical ab initio calculations. Ozone forms a hydrogen bond with the ice surface. Previously to these periodical calculations, the O3•••H2O complexes were modelized. Cyanoacetylene shows two adsorption states on amorphous ice. The first, between 15 and 45 K, is characterized by a hydrogen bond between dangling OH and nitrogen atom of cyanoacetylene. The second, between 45 and 110 K, implies a hydrogen bond between a dangling O of the ice surface and a hydrogen atom of cyanoacetylene. The activation desorption energy for the second state, measured by TPD, is equal to 39 kJ/mol. A proton donor or acceptor character of the cyanoacetylene with ice was observed. These effects also appear in isolated cyanoacetylene∙∙∙water complexes observed in cryogenic matrix. The relative stabilities were determined from ab initio calculations. The kinetic or thermodynamic nature of the adsorption processes was discussed. A preliminary photochemical study of ozone co-adsorbed on ice surface with cyanoacetylene shows that a reaction occurs. This reaction leads to the formation of H2O2, O2 and a third product supposed to be a ketene., L'adsorption de l'ozone et du cyanoacétylène sur une surface de glace amorphe d'eau a été caractérisée par spectrométrie IRTF entre 10 et 180K. L'ozone s'adsorbe sur les OH libres de surface de la glace et une énergie d'activation de désorption de 20 kJ/mol a été mesurée par Désorption Programmée en Température (DPT) couplée à l'IRTF. Cette valeur a été confirmée par des calculs quantiques ab initio de type périodique et l'interaction a été caractérisée comme étant de type liaison hydrogène. En préliminaire au calcul périodique, les complexes O3•••H2O ont également été modélisés. Le cyanoacétylène montre deux états d'adsorption sur la surface de glace amorphe, le premier, entre 15 et 45 K, se caractérise par l'existence d'une liaison hydrogène entre les OH libres de surface de la glace et l'atome d'azote du cyanoacétylène, le second entre 45 et 110 K, met aussi en jeu une liaison hydrogène entre un doublet libre d'un atome d'oxygène de surface de la glace et l'atome d'hydrogène du cyanoacétylène. L'énergie d'activation de désorption pour le deuxième état, déterminée par DPT, est égale à 39 kJ/mol. Un caractère donneur et accepteur de proton du cyanoacétylène vis à vis de la glace est observé. Ces effets apparaîssent aussi lors de l'étude des complexes cyanoacétylène•••eau en matrice d'argon. Les stabilités relatives ont été déterminées par calcul ab initio. La nature cinétique et thermodynamique des processus d'adsorption est discutée. Une étude préliminaire de la photochimie de l'ozone co-adsorbé sur de la glace amorphe avec du cyanoacétylène a montré la formation de H2O2, de O2 et d'un troisième produit de réaction qui pourrait être un cétène.