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Support and promoter effects in the selective oxidation of ethane to acetic acid catalyzed by Mo-V-Nb oxides

Paper ID Volume ID Publish Year Pages File Format Full-Text
43223 45958 2008 9 PDF Available
Title
Support and promoter effects in the selective oxidation of ethane to acetic acid catalyzed by Mo-V-Nb oxides
Abstract

Catalysts based on Mo-V-Nb oxides were examined in bulk and supported forms for the oxidation of ethane to ethene and acetic acid. Bulk Mo0.61V0.31Nb0.08Ox powders showed rates and selectivities similar to those in previous reports. Precipitation in the presence of colloidal TiO2 led to a 10-fold increase in ethene and acetic acid rates (per active oxide) without significant changes in selectivity relative to unsupported samples. Precipitation in the presence of colloidal ZrO2 and Al2O3 suspensions, however, introduced unselective combustion sites without improving ethane oxidation rates. Mo5O14 structures, containing low-valent metal cation centers were detected in bulk Mo0.61V0.31Nb0.08Ox and TiO2-supported samples by Raman and UV–visible spectra and consistent with X-ray diffraction patterns, but not in Al2O3- or ZrO2-containing catalysts. The introduction of trace amounts of Pd (0.0025–0.01 wt.%), as a physical mixture of separate 0.3 wt.% Pd/SiO2, led to the near complete depletion of ethene intermediates and to a significant increase in acetic acid synthesis rate. Small PdOx catalyze ethene oxidation to acetaldehyde, but require the rapid scavenging of these molecules by Mo-V-Nb oxides to prevent acetaldehyde combustion and loss of selectivity. Dispersed VOx domains on TiO2 were able to catalyze all steps required for ethane oxidation to acetic acid. COx selectivities, however, were much higher than on bulk and TiO2-supported Mo0.61V0.31Nb0.08Ox catalysts. Dispersed MoOx domains were essentially inactive at these reaction conditions but their concurrent presence with VOx increased acetic acid selectivity by titrating unselective sites and stabilizing more reducible VOx species.

Graphical abstractThe rate and selectivity of acetic acid synthesis from ethane-O2 reactants were markedly increased by depositing active Mo0.61V0.31Nb0.08Ox onto colloidal TiO2 and combining them with a Pd/SiO2 co-catalyst (≤0.01 wt.% Pd). TiO2 leads to active structures with higher area but surface reactivity similar to that on bulk powders. PdOx species catalyze selective oxidation of ethene intermediates to acetic acid.Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Ethane; Oxidation; Metal oxide; Ethene; Acetic acid
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Support and promoter effects in the selective oxidation of ethane to acetic acid catalyzed by Mo-V-Nb oxides
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 334, Issues 1–2, 1 January 2008, Pages 339–347
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us