Acid sites development on Cr3+/SiO2 catalysts obtained by the sol–gel method and hydrothermal treatment: Effect of calcination temperature

Zapata, Pablo Martín Cuesta; Parentis, Mónica Liliana; Gonzo, Elio Emilio; Bonini, Norberto Alejandro

doi:10.1016/j.apcata.2013.02.028

Cited by 17 publications

(22 citation statements)

References 28 publications

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“…The NH 3 -TPD profile for the reused Cr adsorbent exhibits a low-temperature peak at about 220 °C attributed to weak Lewis type acid sites, and a high-temperature peak above 600 °C, ascribed to the presence of Brönsted acid sites. , This location in acidity is in good agreement with the reported results, whereas the K 2 Cr 2 O 7 impregnated sample (mainly containing Cr(VI) species) shows the presence of the high-temperature peak only (SI Figure S4E). Previous reports have revealed that the development of Lewis acidic centers is directly related to Cr(III) species, while the presence of Cr(VI) induces the appearance of Brönsted acidic centers. , Hence, our NH 3 -TPD results confirm this conclusion.…”

Section: Resultssupporting

confidence: 89%

“…In contrast, as for the (NH 4 ) 2 Cr 2 O 7 impregnated sample, the peaks at 577 and 586 eV, which signify the presence of Cr(III), suggest that the ammonium group causes Cr(VI) to be reduced, which is in conformity with the foregoing analysis. Besides, XRD measurements (SI Figure S4B) confirm that both (NH 4 ) 2 Cr 2 O 7 impregnated sample and the reused Cr adsorbent show the development of Cr 2 O 3 crystalline phase, whereas in the pattern corresponding to the K 2 Cr 2 O 7 impregnated sample, one sharp diffraction peak centered around 2θ = 26° indicates the presence of the CrO 3 phase . These XRD observations are consistent with the XPS results and also verified by the UV–vis DR analysis.…”

Section: Resultssupporting

confidence: 84%

“…Figure C shows the high-angle XRD patterns obtained for the reused Cr adsorbent and the fresh MCM-41sample. From Figure C, a broad band located at 2θ ≈ 25° is characteristic of amorphous silica . Furthermore, for the sample of reused Cr adsorbent, XRD exhibits nine sharp diffraction peaks, which are ascribed to the presence of Cr 2 O 3 crystalline phase .…”

Section: Resultsmentioning

confidence: 93%

“…In recent decades, the use of Cr-MCM-41 has attracted interest as a catalyst. − Generally, the presence of Cr(VI) species introduces favorable redox properties through the system of Cr(VI)/Cr(III) . Meanwhile, the Cr(VI) species are related to the development of Brönsted centers, while the Cr(III) centers contribute to Lewis acidity . Our recent work − and other reports , have shown that redox and acidity properties may play an important role in any methyl mercaptan (CH 3 SH) catalytic elimination system.…”

Section: Introductionmentioning

confidence: 87%

See 3 more Smart Citations

Recycling Spent Cr Adsorbents as Catalyst for Eliminating Methylmercaptan

He¹,

Zhang²,

Zhao³

et al. 2018

Environ. Sci. Technol.

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Waste adsorbents generated from treating Cr(VI)-containing wastewater are hazardous materials and generally landfilled or treated by acid or base desorption, with concomitant high cost and toxic effects. The present work shows that these Cr adsorbents can be reused as highly efficient catalysts for treating sulfur-containing VOCs (CHSH), not only avoiding the economic and environmental impact from the conventional approaches, but also achieving the efficient treatment of sulfur-containing waste gas. Importantly, these reused Cr adsorbents exhibit enhanced activity and stability compared with the catalysts reported elsewhere, indicating a new avenue of green chemistry. The highly toxic adsorbed Cr(VI) species are reduced to a CrO crystalline phase by calcination and finally immobilized as a CrS solid phase while converting and eliminating CHSH. Still, the presence of Cr(VI) species on the reused Cr adsorbent provides enough reactive sites for reaction, but high concentration of Cr(VI) species causes serious accumulation of coke deposit on the catalyst, leading to fast deactivation of the catalyst.

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Section: Resultssupporting

confidence: 89%

Section: Resultssupporting

confidence: 84%

Section: Resultsmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 87%

See 2 more Smart Citations

Recycling Spent Cr Adsorbents as Catalyst for Eliminating Methylmercaptan

He¹,

Zhang²,

Zhao³

et al. 2018

Environ. Sci. Technol.

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show abstract

“…On the other hand, a simultaneous controlled and facile method to obtain the highly dispersed Cr-based catalyst with rich active sites for the DHP reaction is a challenge. At present, the popular methods for synthesizing Cr-based catalysts include the hydrothermal synthesis, , the sol–gel method assisted with a surfactant and/or a solvent, ,, and the impregnation method. , The hydrothermal synthesis can control effectively the size and dispersion of the Cr species through parameters including temperature, time, and raw material ratio. Nevertheless, this method requires harsh preparation conditions and a long time (high pressures and temperatures in a confined space), which restricts its large-scale industrial application.…”

Section: Introductionmentioning

confidence: 99%

Flowing-Air-Induced Transformation to Promote the Dispersion of the CrO_x Catalyst for Propane Dehydrogenation

Zhang

Huang

et al. 2021

ACS Appl. Mater. Interfaces

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Highly dispersed chromium (Cr)-based catalysts are promising candidates for the catalytic dehydrogenation of propane (DHP). However, the easier aggregation of Cr species into crystalline Cr2O3 at the high-temperature calcination and reaction process is a big challenge, which severely restricts the improvement of activity and stability of the DHP reaction. Herein, a flowing-air-induced transformation method was first proposed, and the catalytic performance of the prepared Cr/MCM-41 catalysts was found to be significantly improved compared to that of the Cr-based catalyst prepared by the traditional calcination method, even better than that of most of the reported Cr-based catalysts and some noble metal-based catalysts. X-ray absorption spectroscopy and in situ Raman spectroscopy as well as other characterization techniques demonstrated that the in situ calcination in flowing air could not only effectively restrain the conversion of Cr(VI) into Cr(III) but also largely improve the dispersion of Cr species. Furthermore, DHP activity is found to have a positive correlation with the amount of monomeric Cr(VI) species, which is proved to be the precursor of active coordinatively unsaturated Cr sites. Our proposed flowing-air-induced transformation method provides a general strategy for preparing the highly dispersed Cr-based catalysts and other metal oxide materials with varied valence and exhibits potential application prospects in industry.

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Investigation of the Isolated Cr(VI) Species in Cr/MCM‐41 Catalysts and its Effect on Catalytic Activity for Dehydrogenation of Propane

Zhang

Yang

et al. 2018

ChemCatChem

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Cr‐modified MCM‐41 with different loadings were prepared and tested in the propane dehydrogenation (PDH) reaction. As for Cr/MCM‐41 system, the general knowledge was that high Cr loadings resulted in the reduction of silica surface hydroxyl groups, thus leading to the formation of inactive Cr(III) species, as clusters and/or crystalline Cr2O3. However, in the present work, isolated Cr(VI) states were identified in the Cr/MCM‐41 catalysts, instead of Cr(III) species, using UV‐vis and H2‐TPR. These isolated Cr(VI) species are difficult to reduce, causing the decreased activity for propane conversion and low selectivity towards C3H6 in the PDH process. In contrast, a good dispersion of the Cr species was obtained using a chromium column adsorption process, and the absence of the isolated state of Cr(VI) species on this sample contributed to high activity toward PDH process. The investigation of the isolated Cr(VI) species is very important for the Cr‐based PDH catalyst system.

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Acid sites development on Cr3+/SiO2 catalysts obtained by the sol–gel method and hydrothermal treatment: Effect of calcination temperature

Cited by 17 publications

References 28 publications

Recycling Spent Cr Adsorbents as Catalyst for Eliminating Methylmercaptan

Recycling Spent Cr Adsorbents as Catalyst for Eliminating Methylmercaptan

Flowing-Air-Induced Transformation to Promote the Dispersion of the CrO_x Catalyst for Propane Dehydrogenation

Investigation of the Isolated Cr(VI) Species in Cr/MCM‐41 Catalysts and its Effect on Catalytic Activity for Dehydrogenation of Propane

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Acid sites development on Cr3+/SiO2 catalysts obtained by the sol–gel method and hydrothermal treatment: Effect of calcination temperature

Cited by 17 publications

References 28 publications

Recycling Spent Cr Adsorbents as Catalyst for Eliminating Methylmercaptan

Recycling Spent Cr Adsorbents as Catalyst for Eliminating Methylmercaptan

Flowing-Air-Induced Transformation to Promote the Dispersion of the CrOx Catalyst for Propane Dehydrogenation

Investigation of the Isolated Cr(VI) Species in Cr/MCM‐41 Catalysts and its Effect on Catalytic Activity for Dehydrogenation of Propane

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Flowing-Air-Induced Transformation to Promote the Dispersion of the CrO_x Catalyst for Propane Dehydrogenation