The effect of boron on ZSM-5 zeolite shape selectivity and activity II. Coincorporation of aluminium and boron in the zeolite lattice

Sayed, Moein B.

doi:10.1016/0021-9517(89)90070-5

Cited by 71 publications

(19 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…25 Therefore, rigorous normalization of acid-catalyzed turnover rates in boroaluminosilicates requires discrimination between Brønsted acidic OH groups associated with Al and B heteroatoms, even when the quantity of B heteroatoms is much greater than Al (Al/B < 0.01), because observed catalytic reactivity originates predominantly from protons at framework Al (e.g., n-hexane cracking). 24 Temperature-programmed desorption (TPD) of NH 3 from B−Al−MFI following saturation in aqueous-phase NH 4 NO 3 solution overestimates the number of framework Al heteroatoms, 22 because NH 3 also binds to trigonal and tetrahedral B heteroatoms 33 clusters (Figure 2e−h). These findings are consistent with previous reports of B−Al−MFI zeolites made with similar synthetic protocols, 22 where it was hypothesized that ethylenediamine acts as both a structure directing agent during B− Al−MFI synthesis and as a ZGM by binding to MFI crystal facets during synthesis to influence anisotropic crystal growth.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, rigorous normalization of acid-catalyzed turnover rates in boroaluminosilicates requires discrimination between Brønsted acidic OH groups associated with Al and B heteroatoms, even when the quantity of B heteroatoms is much greater than Al (Al/B < 0.01), because observed catalytic reactivity originates predominantly from protons at framework Al (e.g., n -hexane cracking) . Temperature-programmed desorption (TPD) of NH 3 from B–Al–MFI following saturation in aqueous-phase NH 4 NO 3 solution overestimates the number of framework Al heteroatoms, because NH 3 also binds to trigonal and tetrahedral B heteroatoms and thus the NH 3 evolved during TPD may originate from B or Al heteroatoms. NH 3 titrants can be used to quantify the number protons at framework Al heteroatoms (H + Al ) in B–Al–MFI zeolites either by saturation of B and Al sites with NH 4 + by aqueous-phase ion-exchange and selective removal of NH 3 from B via purging in flowing dry He (433 K), or by saturation in gaseous NH 3 at temperatures that result in selective adsorption at H + Al sites (433 K) .…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Influence of Tetrapropylammonium and Ethylenediamine Structure-Directing Agents on the Framework Al Distribution in B–Al–MFI Zeolites

Hur

Kester

Nimlos

et al. 2019

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

We report synthetic protocols to independently influence composition and crystallite sizes of MFI zeolites, properties that contribute to Thiele moduli, and the proximity of Al heteroatoms at fixed composition (Si/Al ∼ 50). Crystallite sizes decrease with the addition of non-catalytic B heteroatoms in B–Al–MFI zeolites. Using only tetra-n-propylammonium (TPA+) as a structure-directing agent (SDA) leads to occlusion of one TPA+ per channel intersection and a finite percentage of framework Al atoms (20–40%) in proximal configurations. In contrast, using mixtures of ethylenediamine (EDA) and TPA+ (EDA/TPA+ = 15) leads to incorporation of EDA that displaces some TPA+ and to nearly all (>95%) Al in isolated configurations. These findings indicate how adding B and EDA to zeolite synthesis solutions provides a route to crystallizing MFI zeolites of similar composition but with framework Al distributed at varying relative proximity, or with similar Al distributions but different diffusion path lengths.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Influence of Tetrapropylammonium and Ethylenediamine Structure-Directing Agents on the Framework Al Distribution in B–Al–MFI Zeolites

Hur

Kester

Nimlos

et al. 2019

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

show abstract

“…32−34 Moreover, B atoms trigonally coordinated within *BEA frameworks have been reported to appear as tetrahedral in 11 B MAS NMR spectra, depending on the extent of sample hydration. 35 IR OH stretching vibrations of protons at framework Al and B have been observed at ∼3600 and ∼3700 cm −1 , 25,36,37 respectively, but have not been directly quantified to our knowledge in boroaluminosilicates, which would require independent molar extinction coefficients for the two OH groups. Temperature-programmed desorption (TPD) of bases often results in a multitude of desorption features, as observed for ammonia desorption and attributed to acid strength differences between protons compensating framework B and Al.…”

Section: Introductionmentioning

confidence: 97%

Ammonia Titration Methods To Quantify Brønsted Acid Sites in Zeolites Substituted with Aluminum and Boron Heteroatoms

Kester

Miller

Gounder

2018

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

Ammonia titration methods were developed to discriminate and quantify Brønsted acid sites of different strength that compensate aluminum and boron heteroatoms incorporated within zeolite frameworks. Borosilicate and boroaluminosilicate MFI zeolites (B-Al-MFI) were synthesized with different Al contents and crystallite sizes, which are typically correlated structural properties in aluminosilicates synthesized hydrothermally, but independently varied here by incorporating boron as a second framework heteroatom and using ethylenediamine as a structure directing agent. Temperature-programmed desorption (TPD) of ammonia from B-Al-MFI samples saturated via liquid-phase NH4NO3 ion exchange resulted in quantifying the total number of Al and B heteroatoms. In contrast, TPD performed after NH4-form B-Al-MFI samples were purged in flowing helium (433 K), or after gas-phase NH3 adsorption (433 K) onto H-form B-Al-MFI samples, quantified only protons charge-compensating framework Al heteroatoms. Turnover rates for methanol dehydration to dimethyl ether, when measured in zero-order kinetic regimes that are sensitive predominantly to Brønsted acid strength, are dependent only on the number of protons compensating framework Al atoms in B-Al-MFI zeolites. The NH3 titration methods developed here are useful in rigorously normalizing turnover rates of Brønsted acid-catalyzed reactions in boroaluminosilicate zeolites, which have been recognized previously to be dependent solely on Al content. The incorporation of B heteroatoms into zeolite frameworks, which generate protons that are essentially unreactive, provides a strategy to influence crystallite sizes independently of Al content, especially relevant in cases where catalytic behavior is influenced by intracrystalline transport phenomena.

show abstract

“…The selective alkylation of toluene with methanol over the modified HZSM-5 catalyst has been studied extensively for decades. In general, steam treatment, [1] poison treatment of large molecules, [2] modification of Mg, [3,4] B, [5] P, [6] La, [7] Pt, [8] and so forth, and silylation method [9,10] were used to improve porous and acidic properties of the HZSM-5 catalyst to produce PX in concentrations greater than equilibrium concentrations. In addition, methanol reacted partially with toluene to produce alkylbenzenes and the rest was dehydrated to form hydrocarbons by using the methanol-to-hydrocarbon (MTH) process.…”

mentioning

confidence: 99%

Improved Selectivity toward Light Olefins in the Reaction of Toluene with Methanol Over the Modified HZSM‐5 Catalyst

Wang

Wei

et al. 2014

ChemCatChem

View full text Add to dashboard Cite

Light olefins and para-xylene were produced with high selectivity in the reaction of toluene with methanol over a modified HZSM-5 catalyst. Ordered mesoporous structure and weaker acidic sites led to significant contribution to the selectivity toward para-xylene. By means of a single-pulse reaction and the temperature-programmed surface reaction, it was confirmed that the presence of toluene and as-produced xylene shortened the reaction induction period and reduced the formation temperature of ethylene and propylene, which was beneficial to improve the selectivity toward light olefins, particularly ethylene.para-Xylene (PX) is one of the important organic materials used for the synthesis of pure terephthalic acid, which is used to make polyesters, particularly polyethylene terephathalate. In industrial processes, PX is produced from the aromatics of a naphtha catalytic reformer through complicated crystallization or adsorption separation; this method is very costly to obtain the desired purity of more than 99 %. The selective alkylation of toluene with methanol over the modified HZSM-5 catalyst has been studied extensively for decades. In general, steam treatment, [1] poison treatment of large molecules, [2] modification of Mg, [3,4] B, [5] P, [6] La, [7] Pt, [8] and so forth, and silylation method [9,10] were used to improve porous and acidic properties of the HZSM-5 catalyst to produce PX in concentrations greater than equilibrium concentrations. In addition, methanol reacted partially with toluene to produce alkylbenzenes and the rest was dehydrated to form hydrocarbons by using the methanol-to-hydrocarbon (MTH) process. [11] Some studies focused on improving the alkylation reaction as well as restraining side reactions. Thus, a high toluene/methanol molar feed ratio was often used, which would result in low conversion of toluene. However, light olefins, particularly ethylene and propylene, among hydrocarbons were not useless. They were important chemicals for the production of polyethy-lene and polypropylene, and ethylene was also a major component for the production of polyethylene terephathalate. Therefore, it would be meaningful to improve toluene conversion by using an optimum feed ratio of toluene and methanol, to restrain the formation of undesired aromatics with a designed catalyst, as well as to transform the excess methanol (unreacted with toluene) to important chemicals under the same conditions. Hence, we proposed a new mechanism to produce PX with use of extremely high-purity and high-concentration ethylene and propylene in one chemical reaction through the transformation of toluene and methanol (Scheme 1) over the modified HZSM-5 catalyst. It was also of great significance that the two materials used for the production of polyesters-PX and ethylene-could be obtained in one chemical reaction.The modified HZSM-5 catalyst for this process is expected to function in two transformations: one is the alkylation of toluene with methanol to produce PX with high selectivity and the other is the conversion ...

show abstract

The effect of boron on ZSM-5 zeolite shape selectivity and activity II. Coincorporation of aluminium and boron in the zeolite lattice

Cited by 71 publications

References 18 publications

Influence of Tetrapropylammonium and Ethylenediamine Structure-Directing Agents on the Framework Al Distribution in B–Al–MFI Zeolites

Influence of Tetrapropylammonium and Ethylenediamine Structure-Directing Agents on the Framework Al Distribution in B–Al–MFI Zeolites

Ammonia Titration Methods To Quantify Brønsted Acid Sites in Zeolites Substituted with Aluminum and Boron Heteroatoms

Improved Selectivity toward Light Olefins in the Reaction of Toluene with Methanol Over the Modified HZSM‐5 Catalyst

Contact Info

Product

Resources

About