Zinc Oxide–Chromium Oxide Catalysts for Methanol Synthesis

Molstad, M. C.; Dodge, Barnett F.

doi:10.1021/ie50302a005

Cited by 32 publications

(12 citation statements)

References 7 publications

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“…The Zn:Cr ratio was found to significantly influence the catalytic activity of the ZnO/Cr 2 O 3 catalyst . The optimum Zn:Cr ratio has been extensively investigated in the literature. ,, Molstad and Dodge reported that catalysts with Zn:Cr ratios between 70:30 and 60:40 exhibit the highest yield of methanol at relatively low temperatures of 300–325 °C. This observation is in good agreement with the results reported by Bone, who found that the maximum activity is achieved with a Zn-excess catalyst containing about 75 atom % of Zn.…”

Section: Introductionmentioning

confidence: 99%

Spinel-Structured ZnCr₂O₄ with Excess Zn Is the Active ZnO/Cr₂O₃ Catalyst for High-Temperature Methanol Synthesis

et al. 2017

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A series of ZnO/Cr 2 O 3 catalysts with different Zn:Cr ratios was prepared by coprecipitation at a constant pH of 7 and applied in methanol synthesis at 260−300 °C and 60 bar. The X-ray diffraction (XRD) results showed that the calcined catalysts with ratios from 65:35 to 55:45 consist of ZnCr 2 O 4 spinel with a low degree of crystallinity. For catalysts with Zn:Cr ratios smaller than 1, the formation of chromates was observed in agreement with temperature-programmed reduction results. Raman and XRD results did not provide evidence for the presence of segregated ZnO, indicating the existence of Zn-rich nonstoichiometric Zn−Cr spinel in the calcined catalyst. The catalyst with Zn:Cr = 65:35 exhibits the best performance in methanol synthesis. The Zn:Cr ratio of this catalyst corresponds to that of the Zn 4 Cr 2 (OH) 12 CO 3 precursor with hydrotalcitelike structure obtained by coprecipitation, which is converted during calcination into a nonstoichiometric Zn−Cr spinel with an optimum amount of oxygen vacancies resulting in high activity in methanol synthesis. Density functional theory calculations are used to examine the formation of oxygen vacancies and to measure the reducibility of the methanol synthesis catalysts. Doping Cr into bulk and the (10−10) surface of ZnO does not enhance the reducibility of ZnO, confirming that Cr:ZnO cannot be the active phase. The (100) surface of the ZnCr 2 O 4 spinel has a favorable oxygen vacancy formation energy of 1.58 eV. Doping this surface with excess Zn charge-balanced by oxygen vacancies to give a 60% Zn content yields a catalyst composed of an amorphous ZnO layer supported on the spinel with high reducibility, confirming this as the active phase for the methanol synthesis catalyst.

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Section: Introductionmentioning

confidence: 99%

Spinel-Structured ZnCr₂O₄ with Excess Zn Is the Active ZnO/Cr₂O₃ Catalyst for High-Temperature Methanol Synthesis

et al. 2017

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“…Wang and co-workers also reported a bifunctional catalyst (Zr–Zn binary oxide-SAPO-34 zeolite), which has a similar effect on enhancing the selectivity of light olefins as OX-ZEO. Among mixed oxide catalysts, zinc–chromium oxide (ZnCrO x ), as part of a bifunctional catalyst for the conversion of syngas (CO/H 2 ), has been studied since the 1930s. , However, a highly controversial issue is the intermediate that is generated over the ZnCrO x and that entering the zeolite. Specifically, CH 2 CO (ketene) was detected and considered to be a possible intermediate in the work of Bao and co-workers, while CH 3 OH/CH 3 O was pointed out as intermediates by Wang and co-workers.…”

Section: Introductionmentioning

confidence: 99%

Resolving the Intricate Mechanism and Selectivity of Syngas Conversion on Reduced ZnCr₂O_x: A Quantitative Study from DFT and Microkinetic Simulations

et al. 2021

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By combining reduced oxide and zeolite (e.g., ZnCrO x /MSAPO), bifunctional catalysts achieve outstanding olefin selectivity for syngas conversion via a relay process (CO + H2 → IM → olefin) and are one of the hottest catalytic systems. However, the reaction mechanism on the reduced ZnCrO x as well as the intermediate (IM = ketene versus methanol) entering the zeolite are under heated debate owing to the complexity of this system. Herein, we perform systematic density functional theory (DFT) calculations and microkinetic simulations to inspect the possible elementary steps on the highly reduced ZnCr2O4(110) surface, which quantitatively unveils the favored reaction pathways for CO activation and conversion. We find that CO tends to adsorb at the two-coordinate O vacancy sites (VO 2C) and reacts with H at VO 2C to form CHO, while the disproportionation reaction and the direct C–O cleavage are less favored. Importantly, the conversion of CHO plays a vital role in product selectivity; the dissociation of CHO is identified to proceed easily and constitutes a major route responsible for the formation of CH4 and CH2CO, through the following pathway: CHO → CH + O; CH + H → CH2; CH2 + CO → CH2CO; or CH2 + 2H → CH4. Alternatively, CHO could undergo hydrogenation to give CH2O and CH3O intermediates, eventually leading to the formation of CH3OH and CH4. The kinetic analyses on such a complex reaction network disclose that CH4 is the dominant product, while both CH2CO and CH3OH (i.e., two experimentally controversial intermediates) exist in minority with CH2CO being relatively more readily formed. More interestingly, the kinetic model illustrates that the selectivity for CH2CO and the formation of triggered light olefins can be significantly improved over CH4 if a reaction channel converts CH2CO to light olefins when zeolite is added, providing insight into the bifunctionality of the oxide/zeolite system. Also, we demonstrate that high VO 2C coverage is a prerequisite for high activity of CO activation, and the reason for high selectivity of CO2 and low selectivity of H2O is identified to the easier removal of the lattice oxygen by CO to generate CO2 than by H2 to generate H2O. The understanding derived from this work could lay a solid theoretical foundation for comprehending the oxides for the syngas conversion mechanism.

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“…For Pt catalyst, ABS was carried out under relatively high temperature as benzene conversion decreased remarkably at lower temperature, so the desired catalyst to replace should have good thermal stability in order to achieve a high benzene conversion. Zinc/chromium (Zn/Cr) oxide is very stable under high temperatures; therefore, it has been used in similar reactions for one-step conversion of syngas into other hydrocarbons. − The operating temperature (350–450 °C) for Zn/Cr oxide matches well with that (400–500 °C) required for benzene alkylation, − so it would be a good candidate for ABS. Additionally, developing catalysts with higher para -xylene selectivity would be significant, as para -xylene is more valuable.…”

Section: Introductionmentioning

confidence: 99%

One-Step Alkylation of Benzene with Syngas over Non-Noble Catalysts Mixed with Modified HZSM-5

Yang

Fang

Liu

et al. 2019

Ind. Eng. Chem. Res.

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para-Xylene is an important chemical for industry. In this work, alkylation of benzene with syngas (ABS) is carried out to prepare toluene and xylene over zinc/ chromium (Zn/Cr) oxide and modified HZSM-5. The catalyst with a Zn/Cr ratio of 1.6 and 20% (wt) silicate-1 zeolite (S1) coated HZSM-5 has the best catalytic performance, exhibiting 34.4% benzene conversion and 94.7% total selectivity of toluene and xylene, with 73.2% of xylene as para-xylene. The catalyst is carefully characterized; results showed that the activity was enhanced by excessive zinc atoms, which would replace the surface chromium atoms, and this substitution led to more oxygen vacancies. Besides, by coating a layer of S1 on HZSM-5, the production of trimethylbenzene was suppressed and the selectivity of para-xylene among all xylene was increased, due to the coverage of zeolite surface acid sites. These findings are helpful for understanding the one-pot syngas conversion and benzene alkylation processes.

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Zinc Oxide–Chromium Oxide Catalysts for Methanol Synthesis

Cited by 32 publications

References 7 publications

Spinel-Structured ZnCr₂O₄ with Excess Zn Is the Active ZnO/Cr₂O₃ Catalyst for High-Temperature Methanol Synthesis

Spinel-Structured ZnCr₂O₄ with Excess Zn Is the Active ZnO/Cr₂O₃ Catalyst for High-Temperature Methanol Synthesis

Resolving the Intricate Mechanism and Selectivity of Syngas Conversion on Reduced ZnCr₂O_x: A Quantitative Study from DFT and Microkinetic Simulations

One-Step Alkylation of Benzene with Syngas over Non-Noble Catalysts Mixed with Modified HZSM-5

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Zinc Oxide–Chromium Oxide Catalysts for Methanol Synthesis

Cited by 32 publications

References 7 publications

Spinel-Structured ZnCr2O4 with Excess Zn Is the Active ZnO/Cr2O3 Catalyst for High-Temperature Methanol Synthesis

Spinel-Structured ZnCr2O4 with Excess Zn Is the Active ZnO/Cr2O3 Catalyst for High-Temperature Methanol Synthesis

Resolving the Intricate Mechanism and Selectivity of Syngas Conversion on Reduced ZnCr2Ox: A Quantitative Study from DFT and Microkinetic Simulations

One-Step Alkylation of Benzene with Syngas over Non-Noble Catalysts Mixed with Modified HZSM-5

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Spinel-Structured ZnCr₂O₄ with Excess Zn Is the Active ZnO/Cr₂O₃ Catalyst for High-Temperature Methanol Synthesis

Spinel-Structured ZnCr₂O₄ with Excess Zn Is the Active ZnO/Cr₂O₃ Catalyst for High-Temperature Methanol Synthesis

Resolving the Intricate Mechanism and Selectivity of Syngas Conversion on Reduced ZnCr₂O_x: A Quantitative Study from DFT and Microkinetic Simulations