Catalysts For Conversion Of Syngas Research Articles

Hydrocarbon Formation from Syngas with In-Operando Monitoring of Cobalt- and Manganese-Based (pre)Catalysts Using X-ray Diffraction.

Two-layered metal oxides (LiCoO2 and cobalt-doped K n MnO2, n < 1) were explored as precatalysts for nanoconfined cobalt-based Fischer-Tropsch catalysts for conversion of syngas (CO and H2) to hydrocarbons. Ex situ, in situ, and PDF XRD analyses are presented. Based on in situ XRD analysis, LiCoO2 underwent reduction to predominantly cubic and hexagonal phases of cobalt metal. Reaction with syngas resulted in the generation of carbon, cobalt carbide, and lithium carbonate, in addition to the metallic cobalt phases. In the case of cobalt-doped birnessite, catalyst activation converted the birnessite phase to manganite and the cobalt to elemental cobalt, along with similar lithium and carbon phases. Conversion of syngas to C1 through C7 products was observed. The best conversions were observed for the LiCoO2 precursor catalyst, with generally a low olefin-to-paraffin ratio. While the conversions for the cobalt-doped birnessite precatalyst were generally lower, with lower chain lengths (up to C5), these catalysts gave a strikingly high olefin-to-paraffin ratio: in the best case, greater than 20:1.

Insights into the Mn-doping effects on the catalytic performance of ZnCrAlOy/SAPO-34 bifunctional catalyst for the direct conversion of syngas to light olefins

Direct conversion of syngas to light olefins (C2=-C4=) over oxide-zeolite bifunctional catalyst provides a new strategy for light olefins production. Herein, we report a series of bifunctional catalysts composed of SAPO-34 zeolite and Mn-doped ZnCrAlOy oxide with the Mn/Cr ratio ranging from 0 to 0.3 for directing conversion of syngas to light olefins. We achieved a C2=-C4= selectivity of 78.60% (free of CO2) in all hydrocarbon products with a CO conversion of 23.53% and STY of 0.19 g/h·gcat. No obvious deactivation was observed after 220 h reaction. The impact of Mn doping on the physicochemical properties of ZnCrAlOy spinel oxides was explored by various in-situ and ex-situ characterizations. It was found that the Mn doping could decrease the particle size of ZnCrAlOy spinel, which leads to the formation of more oxygen vacancies on the surface of catalyst. The oxygen vacancies (Odef/Olatt) were increased from 0.34 to 0.41 when the Mn content ranges from 0 to 0.2. The abundant oxygen vacancies are beneficial to protect more light olefins and intermediate from hydrogenation. These findings are significant for the further development of high-efficiency bifunctional catalysts for the conversion of syngas to hydrocarbons.

Insights into the size effect of ZnCr2O4 spinel oxide in composite catalysts for conversion of syngas to aromatics

Direct conversion of syngas to aromatics (STA) over oxide-zeolite composite catalysts is promising as an alternative method for aromatics production. However, the structural effect of the oxide component in composite catalysts is still ambiguous. Herein, we investigate the size effect by selecting ZnCr2O4 spinel, as a probe oxide, mixing with H-ZSM-5 zeolite as a composite catalyst for STA reaction. The CO conversion, aromatics selectivity and space-time yield (STY) of aromatics are all significantly improved with the crystal size of ZnCr2O4 oxide decreases, which can mainly attribute to the higher oxygen vacancy concentration and thus the rapid generation of more C1 oxygenated intermediate species. Based on the understanding of the size–performance relationship, ZnCr2O4-400 with a smaller size mixing with H-ZSM-5 can achieve 32.6% CO conversion with 76% aromatics selectivity. The STY of aromatics reaches as high as 4.79 mmol gcat−1 h−1, which outperforms the previously reported some typical catalysts. This study elucidates the importance of regulating the size of oxide to design more efficient oxide-zeolite composite catalysts for conversion of syngas to value-added chemicals.

Enhanced Catalytic Performance of CuO–ZnO–Al2O3/SAPO-5 Bifunctional Catalysts for Direct Conversion of Syngas to Light Hydrocarbons and Insights into the Role of Zeolite Acidity

Synthesis of light hydrocarbons from synthesis gas using bifunctional catalysts consisting of CuO–ZnO–Al2O3 methanol synthesis catalysts and SAPO-5 were investigated in a fixed bed reactor. The operating results showed that both the temperature and the ratio of CZA/SAPO-5 influenced the CO conversion and the selectivity of the catalysts. The effects of different dehydration component such as HZSM-5, HMOR and SAPO-5 and subsequently the impact of the zeolite acidity on the catalytic performance were also investigated. Experimental results indicated that zeolites in bifunctional catalysts played the crucial role for the distribution of hydrocarbons, and SAPO-5 was superior to the other zeolites in terms of better conversion and C3–C5 selectivity due to its suitable topology and proper acidic property. The efficiency of the CZA/SAPO-5 catalysts was found to be directly proportional to the Bronsted acid sites density of the zeolite and Bronsted acid sites are the likely zeolite active sites for DME dehydration. High time–space yield (461.6 mg mL−1 h−1) and high selectivity (88.1%) of light hydrocarbons (C3–C5) could be achieved on the CZA/SAPO-5-0.4 catalyst at 290 °C.

Impact of Niobium in the Metal\u2013Organic Framework-Mediated Synthesis of Co-Based Catalysts for Synthesis Gas Conversion

We report the use of transition metal precursors impregnated into the pores of CPO-27(Co) metal–organic framework (MOF) crystals prior to pyrolysis as a straightforward strategy for tuning the properties of MOF-derived Co-based catalysts. By adding a Nb inorganic salt prior to pyrolysis hierarchical pores are formed in the resulting carbon and the Co accessible surface area is greatly increased leading to a strong enhancement of CO hydrogenation activity.Graphic Enhancing the activity of MOF-MS Co catalysts for syngas conversion by introducing Nb by impregnation into the pores of CPO-27(Co).

Activation of CO and surface carbon species for conversion of syngas to light olefins on ZnCrOx-Al2O3 catalysts

As an effective part of the bifunctional catalyst for conversion of syngas to light olefins, ZnCrOx-Al2O3 mixed oxides were studied using surface sensitive techniques of X-ray photoelectron spectroscopy (XPS) and high-sensitivity low-energy ion scattering spectroscopy (HS-LEIS), as well as in situ Fourier Transform infrared spectroscopy (FTIR) and temperature-programmed desorption (TPD). Reducing and oxidizing treatments induce significant changes of the top-surface compositions as observed by HS-LEIS. After CO/H2 treatment, an obvious amount of dissociated carbon and oxygen-containing carbon species were evidenced on the surface by XPS and HS-LEIS. The oxygen-containing carbon species include bicarbonate, carbonate and formate, and can be efficiently removed under H2. Formate species may be formed by hydrogenation of the carbonate and bicarbonate species, and can be removed to regenerate the active sites for CO dissociation. TPD results under H2 atmosphere show the production of methane, ethane and methanol for the surface pre-treating in CO at 300 °C.

Characterization and testing of silica-supported cobalt–palladium catalysts for conversion of syngas to oxygenates

Silica-supported Co–Pd catalysts were prepared by co-impregnation using 2wt% Pd and two different cobalt loadings: 2wt% (2Co–2Pd) and 10wt% (10Co–2Pd). They were characterized by ICP-OES, H2-TPR, in situ XRD, DRIFTS, and activity/selectivity in CO hydrogenation. Activity/selectivity studies showed that the 10Co–2Pd catalyst is more active for CO hydrogenation with high selectivity toward hydrocarbons, while 2Co–2Pd catalyst shows higher selectivity toward oxygenates, but considerably lower overall activity. DRIFTS studies for 10Co–2Pd catalyst at 230°C indicated that sites at which CO adsorbs linearly are the main active sites for CO hydrogenation, which leads toward formation of hydrocarbons. On the other hand, the bridged sites were found to be the main active sites for 2Co–2Pd catalyst, which leads to increased selectivity toward oxygenated compounds. The hydrogenation of CO adsorbed on these bridge sites was found to be much slower, explaining the low activity of this catalyst.

Conversion of syngas to higher alcohols over Cu-Fe-Zr catalysts induced by ethanol

Ethanol induced method was applied to prepare Cu-Fe-Zr catalysts for conversion of syngas to higher alcohols. The catalytic performance of the catalysts induced by ethanol was superior to that of the catalyst prepared by the conventional precipitation method. Among various procedures for ethanol induced method, it was found that incorporation of ethanol in the precipitation process was the better. After incorporation of ethanol, the crystal size of CuO decreased and the reduction of copper species became easier. The better activity of Cu-Fe-Zr catalysts prepared by ethanol induced procedures was probably caused by the higher dispersion of Cu species.