Qiang Guo

Sustainable Synthesis of Zeolites without Addition of Both Organotemplates and Solvents

The development of sustainable and environmentally friendly techniques for synthesizing zeolites has attracted much attention, as the use of organic templates and solvents in the hydrothermal synthesis of zeolites is a major obstacle for realizing green and sustainable synthesis ways. Recently, the introduction of the organotemplate-free synthesis method allowed avoiding the use of organic templates, but water as solvent was still required; solvent-free routes on the other hand beared the potential to significantly reduce the amount of polluted wastewater, but organic templates were still present. In this work, we have demonstrated a combined strategy of both organotemplate- and solvent-free conditions to synthesize aluminosilicate zeolites Beta and ZSM-5 (S-Beta and S-ZSM-5), two of the most important zeolites relevant for industry. The samples are thoroughly characterized by XRD patterns, SEM images, N2 sorption isotherms, UV-Raman spectra, and (29)Si and (27)Al MAS NMR spectra. The results demonstrate that S-Beta and S-ZSM-5 zeolites exhibit almost the same textural parameters (e.g., BET surface area and pore volume) and catalytic performance in cumene cracking and m-xylene isomerization as those of conventional Beta and ZSM-5 zeolites synthesized under hydrothermal conditions (C-Beta and C-ZSM-5). The organotemplate- and solvent-free syntheses of S-Beta and S-ZSM-5 take place at a low-pressure regime and are free of harmful gases as well as give high product yields together with highly efficient consumption of the starting raw materials. These advantages plus the very simple procedures opened the pathway to a highly sustainable zeolite synthesis protocol compared to conventional methods currently employed for C-Beta and C-ZSM-5. Very interestingly, this simple synthesis is a good model for understanding zeolite crystallization. The detail characterizations indicate that the S-Beta crystals are formed from the assembly of zeolite building units, mainly 4MRs, while the 5MRs in the framework are just formed in the crystallization of S-ZSM-5, rather than existence in the starting solid mixture. During the crystallization processes, small traces of water play an important role for the hydrolysis and condensation of silica and/or aluminosilicate species.

Highly Active and Recyclable Sn-MWW Zeolite Catalyst for Sugar Conversion to Methyl Lactate and Lactic Acid

Highly active and recyclable sn-mww zeolite catalyst for sugar conversion to methyl lactate and lactic acid

In situ UV Raman spectroscopic study on the synthesis mechanism of AlPO-5.

Despite these efforts, a thorough understandingof the template effect, particularly the significance of the roleof templating in the channel formation of aluminophosphatemolecular sieves, is still lacking because of the complexity ofthe synthesis process.Avery powerful but relatively unexplored way of probingthis process is to perform in situ characterization underworking conditions.

A Thorough Investigation of the Active Titanium Species in TS‐1 Zeolite by In Situ UV Resonance Raman Spectroscopy

A thorough investigation of the active titanium species in TS-1 zeolite was conducted by in situ UV resonance Raman spectroscopy combined with UV/Vis diffuse reflectance spectroscopy, DFT calculations, and epoxidation experiments. A new titanium species was identified with a characteristic Raman band at 695 cm(-1) when excited at the 266 nm laser line. It is shown that the newly found titanium species is active in the epoxidation reactions in addition to the tetrahedrally coordinated titanium species. However, the acidity of the new titanium species could catalyze the ring-opening reactions of the epoxy products. It results in a lower selectivity toward the epoxy products relative to that of the tetrahedrally coordinated titanium species. The side reaction can be suppressed by the addition of a weak basic reagent.

UV-Raman and NMR spectroscopic studies on the crystallization of zeolite A and a new synthetic route.

UV-Raman and NMR spectroscopy, combined with other techniques, have been used to characterize crystallization of zeolite A. In situ UV-Raman spectroscopy shows that the starting gel for crystallization of zeolite A contains a lot of four-ring (4R) building units and the appearance of six-ring (6R) building blocks is the signal for crystal formation. (29)Si NMR spectroscopy results suggest that the starting gel is double four-ring (D4R) rich and during crystallization of zeolite A both α and β cages appear. (27)Al NMR spectroscopy results indicate the absence of Al (2Si) species in the starting gel, suggesting the absence of single 4R building units in the starting gel. Furthermore, composition analysis of both solid and liquid samples shows that the solid rather than liquid phase predominates for the crystallization of zeolite A. Therefore, it is proposed that the crystallization of zeolite A mainly occurs in the solid phase by self-assembly or rearrangement starting from the zeolite building units mainly consisting of D4R. The essential role of D4R is directly confirmed by successful conversion from a solution of D4R to zeolite A in the presence of NaCl, and the importance of solid phase is reasonably demonstrated by the successful synthesis of zeolite A from a dry aluminosilicate gel. By considering that the solid phase has a major contribution to crystallization, a novel route was designed to synthesizing zeolite A from the raw materials water glass (Na(2)SiO(3) in aqueous solution) and NaAlO(2), without additional water and NaOH; this route not only simplifies synthetic procedures, but reduces water consumption.

Organotemplate-free and one-pot fabrication of nano-rod assembled plate-like micro-sized mordenite crystals

Plate-like micro-sized MOR and Fe-MOR zeolite crystals assembled from highly uniform nano-rods are successfully fabricated by an organotemplate-free method during one-pot crystallization in the presence of a MOR seed solution. The seed solution rich in 4-membered rings plays a critical role for the formation of the unique nano-rod assembled structure.

UV Raman Spectroscopic Studies on the Synthesis Mechanism of FeAlPO4-5

Abstract FeAlPO4-5 samples with various iron contents were investigated by UV resonance Raman spectroscopy and UV-Vis spectroscopy. The Raman spectra of FeAlPO4-5 show four feature bands related to the framework iron at 630, 1060, 1140, and 1210 cm−1 when excited by 266 nm laser. It is found that only part of ferric ions could enter into the framework, while the others exist in the extra-framework in the form of six-coordinated state. This kind of iron gives characteristic Raman band at 285 cm−1. Combined with UV resonance Raman spectroscopy, UV-Vis spectroscopy, and X-ray diffraction, the crystallization process of FeAlPO4-5 (Al/Fe = 760) was studied. It is found that, in the early stages of the crystallization, the iron species exist in the form of six-coordinated state while attached to the end of the 1-dimensional AlPO4 chain. The Fe–O bonds in the six-coordinated state hamper the crystallization of AlPO4. The crystallization of the FeAlPO4-5 began when the reaction between the 1-dimensional AlPO4 chains occurred. At the same time, the six-coordinated ferric ions converted to the tetrahedral iron.