Alkylation reactions over ion-exchanged molecular sieve zeolite catalysts. Part 1.—Alkylation of toluene with methanol: consideration of the effects of reaction parameters on catalyst deactivation and the extent of polysubstitution

1983 ◽  
Vol 79 (2) ◽  
pp. 281 ◽  
Author(s):  
Brendan Coughlan ◽  
William M. Carroll ◽  
John Nunan
Keyword(s):  
Molecular Sieve ◽  
Catalyst Deactivation ◽  
Zeolite Catalysts ◽  
Reaction Parameters ◽  
Alkylation Reactions

Para-directed aromatic reactions over shape-selective molecular sieve zeolite catalysts

1979 ◽  
Vol 101 (22) ◽  
pp. 6783-6784 ◽  
Author(s):  
N. Y. Chen ◽  
W. W. Kaeding ◽  
F. G. Dwyer
Keyword(s):  
Molecular Sieve ◽  
Zeolite Catalysts ◽  
Shape Selective

scholarly journals Contrasting Arene, Alkene, Diene, and Formaldehyde Hydrogenationin H-ZSM-5, H-SSZ-13, and H-SAPO-34 Zeolite Frameworks during MTO

2019 ◽  
Author(s):  
Mykela DeLuca ◽  
Christina Janes ◽  
David Hibbitts
Keyword(s):  
Selective Hydrogenation ◽  
Density Functional ◽  
High Pressures ◽  
Catalyst Deactivation ◽  
Zeolite Catalysts ◽  
Functional Theory ◽  
As Species ◽  
Methanol To Olefin ◽  
Alkene Hydrogenation ◽  
Thermodynamic Instability

<p>Co-feeding H<sub>2</sub> at high pressures increases zeolite catalyst lifetimes during methanol-to-olefin (MTO) reactions while maintaining high alkene-to-alkane ratios; however, the mechanisms and species hydrogenated by H<sub>2</sub> co-feeds to prevent catalyst deactivation remain unknown. This study uses periodic density functional theory (DFT) to examine hydrogenation mechanisms of MTO product C<sub>2</sub>–C<sub>4</sub> alkenes, as well as species related to the deactivation of MTO catalysts such as C<sub>4</sub> and C<sub>6</sub> dienes, benzene, and formaldehyde in H-MFI and H-CHA zeolite catalysts. Results show that dienes and formaldehyde are selectively hydrogenated in both frameworks at MTO conditions because their hydrogenation transition states proceed via allylic and oxocarbenium cations which are more stable than alkylcarbenium ions which mediate alkene hydrogenation. Diene hydrogenation is further stabilized by protonation and hydridation at α,δ positioned C-atoms to form 2-butene from butadiene and 3-hexene from hexadiene as primary hydrogenation products. This α,δ-hydrogenation directly leads to selective hydrogenation of dienes; pathways which hydrogenate dienes at the α,β-position (e.g., forming 1-butene from butadiene) proceed with barriers 20 kJ mol<sup>-1</sup> higher than α,δ-hydrogenation and with barriers nearly equivalent to butene hydrogenation, despite α,β-hydrogenation of butadiene also occurring through allylic carbocations. Hydrogenation of formaldehyde, a diene precursor, occurs with barriers that are within 15 kJ mol<sup>-1</sup> of diene hydrogenation barriers, indicating that it may also contribute to increasing catalyst lifetimes by preventing diene formation. Benzene, in contrast to dienes and formaldehyde, is hydrogenated with higher barriers than C<sub>2</sub>–C<sub>4</sub> alkenes despite proceeding via stable benzenium cations because of the thermodynamic instability of the product which has lost aromaticity. Carbocation stabilities predict the relative rates of alkene hydrogenation and in some cases shed insights into the hydrogenation of benzene, dienes, and formaldehyde, but cation stabilities alone cannot account for the poor hydrogenation of benzene or the facile hydrogenation of dienes, boosted by stabilization conferred by a,δ-hydrogenation. This work suggests that the main mechanisms of catalyst lifetime improvement with high H<sub>2</sub> co-feeds is reduction of diene concentrations through both their selective hydrogenation and hydrogenation of their precursors to prevent formation of deactivating polyaromatic species.</p>

scholarly journals Deactivation and Regeneration of Zeolite Catalysts Used in Pyrolysis of Plastic Wastes—A Process and Analytical Review

Catalysts ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 770
Author(s):  
Vivien Daligaux ◽  
Romain Richard ◽  
Marie-Hélène Manero
Keyword(s):  
Catalyst Deactivation ◽  
Structural Characteristics ◽  
Deep Understanding ◽  
Analytical Techniques ◽  
Reaction Rates ◽  
Zeolite Catalysts ◽  
Coke Deposition ◽  
Oh Radicals ◽  
Major Drawback ◽  
Solid Catalysts

In catalytic industrial processes, coke deposition remains a major drawback for solid catalysts use as it causes catalyst deactivation. Extensive study of this phenomenon over the last decades has provided a better understanding of coke behavior in a great number of processes. Among them, catalytic pyrolysis of plastics, which has been identified as a promising process for waste revalorization, is given particular attention in this paper. Combined economic and environmental concerns rose the necessity to restore catalytic activity by recovering deactivated catalysts. Consequently, various regeneration processes have been investigated over the years and development of an efficient and sustainable process remains an industrial challenge. Coke removal can be achieved via several chemical processes, such as oxidation, gasification, and hydrogenation. This review focuses on oxidative treatments for catalyst regeneration, covering the current progress of oxidation treatments and presenting advantages and drawbacks for each method. Molecular oxidation with oxygen and ozone, as well as advanced oxidation processes with the formation of OH radicals, are detailed to provide a deep understanding of the mechanisms and kinetics involved (direct and indirect oxidation, reaction rates and selectivity, diffusion, and mass transfer). Finally, this paper summarizes all relevant analytical techniques that can be used to characterize deactivated and regenerated solid catalysts: XRD, N2 adsorption-desorption, SEM, NH3-TPD, elemental analysis, IR. Analytical techniques are classified according to the type of information they provide, such as structural characteristics, elemental composition, or chemical properties. In function of the investigated property, this overall tool is useful and easy-to-use to determine the adequate analysis.

Synthesis of Novel Ag Modified MCM-41 Mesoporous Molecular Sieve and Beta Zeolite Catalysts for Ozone Decomposition at Ambient Temperature

2004 ◽  
Vol 98 (1) ◽  
pp. 57-60 ◽  
Author(s):  
Narendra Kumar ◽  
Petya M. Konova ◽  
Anton Naydenov ◽  
Teemu Heikill� ◽  
Tapio Salmi ◽  
...  
Keyword(s):  
Ambient Temperature ◽  
Molecular Sieve ◽  
Mesoporous Molecular Sieve ◽  
Zeolite Catalysts ◽  
Beta Zeolite ◽  
Ozone Decomposition ◽  
Mcm 41

Kinetic Study of the Simultaneous Cracking of Paraffins and Methanol on HZSM-5 Zeolite Catalysts

2007 ◽  
Vol 5 (1) ◽  
Author(s):  
Diana Mier ◽  
Andrés Tomás Aguayo ◽  
Alaitz Atutxa ◽  
Ana G Gayubo ◽  
Javier Bilbao
Keyword(s):  
Kinetic Model ◽  
Catalyst Deactivation ◽  
Fixed Bed ◽  
Acid Catalyst ◽  
Product Distribution ◽  
Operating Conditions ◽  
Zeolite Catalysts ◽  
Fixed Bed Reactor ◽  
Light Olefins ◽  
Feed Temperature

A study has been carried out on the effect of acid catalyst properties and operating conditions (methanol/n-butane ratio in the feed, temperature, space time, time on stream) on the yield of light olefins (C2-C4) in the simultaneous cracking of n-butane and methanol. The operation has been carried out in an isothermal fixed bed reactor in the 400-575 °C range, using catalysts prepared based on HZSM-5 zeolites (with different Si/Al ratio), HY, Ni/HZSM-5 and SAPO-18. The results are evidence of a synergism between the transformation reactions of both reactants, whose consequence is an increase in the yield of olefins that correspond to the transformation of methanol and the cracking of n-butane. Furthermore, catalyst deactivation by coke is significantly attenuated compared to the corresponding transformation of methanol. Based on the effect of operating conditions on product distribution, a kinetic model is proposed by combining the schemes corresponding to the transformation of individual components.

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