Relationship between Acidity and Activity on Propane Conversion over Metal-Modified HZSM-5 Catalysts

A systematic study of the comparative performances of different metal-impregnated HZSM-5 catalysts (Zn, Ga, Mo, Co, and Zr) for propane conversion is presented. The physicochemical properties of catalysts were characterized by means of XRD, BET, SEM, TEM, FTIR, XPS, 27Al MAS NMR, NH3-TPD and Py-FTIR. It was found that the acidities of the catalysts were significantly influenced by loading metal. More specifically, Mo-, Co- or Zr-modified catalysts showed a large metal size and low acidic density, resulting high olefin selectivity, while Zn- or Ga-modified catalysts maintained their small metal size and acidic density, and mainly reduced B/L due to the Lewis acid sites created by Zn or Ga species, resulting in high aromatics selectivity. Experimental results also showed that there is a balance between metals size and medium and strong acidity on propane conversion. Moreover, based on the different acidity of metal-modified HZSM-5 catalysts, the mechanism of propane conversion was also discussed.

Fischer–Tropsch Synthesis for Light Olefins from Syngas: A Review of Catalyst Development

Light olefins as one the most important building blocks in chemical industry can be produced via Fischer–Tropsch synthesis (FTS) from syngas. FT synthesis conducted at high temperature would lead to light paraffins, carbon dioxide, methane, and C5+ longer chain hydrocarbons. The present work focuses on providing a critical review on the light olefin production using Fischer–Tropsch synthesis. The effects of metals, promoters and supports as the most influential parameters on the catalytic performance of catalysts are discussed meticulously. Fe and Co as the main active metals in FT catalysts are investigated in terms of pore size, crystal size, and crystal phase for obtaining desirable light olefin selectivity. Larger pore size of Fe-based catalysts is suggested to increase olefin selectivity via suppressing 1-olefin readsorption and secondary reactions. Iron carbide as the most probable phase of Fe-based catalysts is proposed for light olefin generation via FTS. Smaller crystal size of Co active metal leads to higher olefin selectivity. Hexagonal close-packed (HCP) structure of Co has higher FTS activity than face-centered cubic (FCC) structure. Transition from Co to Co3C is mainly proposed for formation of light olefins over Co-based catalysts. Moreover, various catalysts’ deactivation routes are reviewed. Additionally, techno-economic assessment of FTS plants in terms of different costs including capital expenditure and minimum fuel selling price are presented based on the most recent literature. Finally, the potential for global environmental impacts associated with FTS plants including atmospheric and toxicological impacts is considered via lifecycle assessment (LCA).

In Situ Formation of a Sub-Nanometer Iridium Phosphide Catalyst from Supported Organometallic Species

<p>While several metal phosphides have attracted significant attention in the last several years due to their potential use as photocatalytic and hydrotreating catalysts, iridium phosphide has remained largely unexplored. In this work, silica-supported pincer-iridium species are thermolyzed, resulting in deconstruction of the tridentate ligand precursor and formation of a sub-nanometer iridium phosphide phase characterized by ³¹P magic angle spinning nuclear magnetic resonance (³¹P-MAS-NMR), X-ray absorption spectroscopy (XAS), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The support material was found to play an active role in determining the product of the surface thermolysis, with the silica supported material generating phosphorus rich iridium phosphide nanoparticles. The resulting silica-supported iridium phosphide phase is explored as a thermocatalyst for non-oxidative butane dehydrogenation, achieving high initial reaction rates up to 900 mol_butenes mol_catalyst^-1 hr^-1and a terminal olefin selectivity of up to 70 %.</p>

In Situ Formation of a Sub-Nanometer Iridium Phosphide Catalyst from Supported Organometallic Species

<p>While several metal phosphides have attracted significant attention in the last several years due to their potential use as photocatalytic and hydrotreating catalysts, iridium phosphide has remained largely unexplored. In this work, silica-supported pincer-iridium species are thermolyzed, resulting in deconstruction of the tridentate ligand precursor and formation of a sub-nanometer iridium phosphide phase characterized by ³¹P magic angle spinning nuclear magnetic resonance (³¹P-MAS-NMR), X-ray absorption spectroscopy (XAS), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The support material was found to play an active role in determining the product of the surface thermolysis, with the silica supported material generating phosphorus rich iridium phosphide nanoparticles. The resulting silica-supported iridium phosphide phase is explored as a thermocatalyst for non-oxidative butane dehydrogenation, achieving high initial reaction rates up to 900 mol_butenes mol_catalyst^-1 hr^-1and a terminal olefin selectivity of up to 70 %.</p>

Control of Sequential MTO Reactions through an MFI-Type Zeolite Membrane Contactor

A membrane for controlling methanol-to-olefin (MTO) reactions was developed, which featured an MFI-type zeolite membrane (Si/Al = 25) that was synthesized on a porous α-alumina substrate using a secondary growth method. Here, the H2/SF6 permeance ratios were between 150 and 450. The methanol conversion rate was 70% with 38% ethylene selectivity and 28% propylene selectivity as determined using a cross-flow membrane contactor. In order to improve the olefin selectivity of the membrane, the MFI zeolite layer (Si/Al = ∞) was coated on an MFI-type zeolite membrane (Si/Al = 25). Using this two-layered membrane system, the olefin selectivity value increased to 85%; this was 19% higher than the value obtained during the single-layer membrane system.

Effect of Reduction of Pt–Sn/α-Al2O3 on Catalytic Dehydrogenation of Mixed-Paraffin Feed

The effect of the Pt–Sn/α-Al2O3 catalyst reduction method on dehydrogenation of mixed-light paraffins to olefins has been studied in this work. Pt–Sn/α-Al2O3 catalysts were prepared by two different methods: (a) liquid phase reduction with NaBH4 and (b) gas phase reduction with hydrogen. The catalytic performance of these two catalysts for dehydrogenation of paraffins was compared. Also, the synergy between the catalyst reduction method and mixed-paraffin feed (against individual paraffin feed) was studied. The catalysts were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) analysis. The individual and mixed-paraffin feed dehydrogenation experiments were carried out in a packed bed reactor fabricated from Inconel 600, operating at 600 °C and 10 psi pressure. The dehydrogenation products were analyzed using an online gas chromatograph (GC) with flame ionization detector (FID). The total paraffin conversion and olefin selectivity for individual paraffin feed (propane only and butane only) and mixed-paraffin feed were compared. The conversion of propane only feed was found to be 10.7% and 9.9%, with olefin selectivity of 499% and 490% for NaBH4 and hydrogen reduced catalysts, respectively. The conversion of butane only feed was found to be 24.4% and 23.3%, with olefin selectivity of 405% and 418% for NaBH4 and hydrogen reduced catalysts, respectively. The conversion of propane and butane during mixed-feed dehydrogenation was measured to be 21.4% and 30.6% for the NaBH4 reduced catalyst, and 17.2%, 22.4% for the hydrogen reduced catalyst, respectively. The olefin selectivity was 422% and 415% for NaBH4 and hydrogen reduced catalysts, respectively. The conversions of propane and butane for mixed-paraffin feed were found to be higher when compared with individual paraffin dehydrogenation. The thermogravimetric studies of used catalysts under oxygen atmosphere showed that the amount of coke deposited during mixed-paraffin feed is less compared with individual paraffin feed for both catalysts. The study showed NaBH4 as a simple and promising alternative reduction method for the synthesis of Pt–Sn/Al2O3 catalyst for paraffin dehydrogenation. Further, the studies revealed that mixed-paraffin feed dehydrogenation gave higher conversions without significantly affecting olefin selectivity.

The effect of steam on maximizing light olefin production by cracking of ethanol and oleic acid over mesoporous ZSM-5 catalysts

Steam cracking significantly improved light olefin selectivity: mainly ethylene was obtained from ethanol and propylene from oleic acid.

Effect of ZSM-5 Acidity in Enhancement of Methanol-to-Olefins Process

The skyrocketing demand for olefins especially propylene, have necessitated continuous efforts in finding alternate route for olefins production. Hence, methanol to olefins (MTO) was recognized as a feasible process since methanol could simply be mass produced from any gasifiable carbon-based feedstock, such as natural gas, coal, and biomass. Essentially, obtaining a more stable catalyst would improve economy of the MTO process. Acidity of catalyst has major influence in MTO, thus it is an indispensable parameter for conversion of methanol into value-added products. The present paper discusses the reactions involved in MTO process and the effect of acidity in enhancement of light olefin selectivity and catalytic stability. The paper also captured perspectives of crucial research and future direction for catalysts development and technologies that can potentiallly boost olefin production and make it competitive with the conventional olefin production processes.