Syngas to Olefins over a CrMnGa/SAPO-34 Bifunctional Catalyst: Effect of Cr and Cr/Mn Ratio

Abstract

Metal oxide in a bifunctional catalyst plays crucial roles in catalytic activity for syngas conversion to olefin (STO).Here, ternary co-precipitated CrMnGa oxides with various Cr/Mn ratios were prepared and combined with SAPO-34 for an STO reaction. By adjusting the Cr:Mn:Ga atomic ratio to 3:2:1, a high CO conversion (43.5%) with light olefin selectivity (87.0%, CO 2 free) is achieved under the reaction conditions of 400 °C, 3.0 MPa, and 3000 mL•h −1 •g −1 . The increase in the Cr/Mn ratio facilitated the CrMnGa catalyst reduction and enhanced surface oxygen vacancies contents and H 2 dissociation ability. The mechanism reveals that *CH 3 O species act as the reaction intermediate for the reaction of CO with the surface OH group and the subsequent hydrogenation. More importantly, the introduction of Cr enhanced the CO activation ability at high temperatures and thus provided a well temperature match for intermediate generation over CrMnGa oxide and further transformation into light olefin over SAPO-34. This study provides a strategy for rational design of highly active metal oxides, which could be used to combine with other zeolites for syngas conversion to high value-added chemicals.

Disentangling the activity-selectivity trade-off in catalytic conversion of syngas to light olefins

“…Recently, the technology was successfully demonstrated in a pilot plant with 1000 ton/year light-olefins output in Shaanxi, China (7,17). Extensive efforts have been made to optimize the catalysts by screening a wide range of metal oxide and zeolite (zeotype) combinations as well as reaction conditions (7,16,(18)(19)(20)(21)(22)(23)(24). As a result, the catalytic performance has been greatly improved; CO conversion could be increased from 17 to 60% with light-olefins selectivity being maintained at 75%, and the yield of light olefins improved from 8 to 27% (16,21,24).…”

Tuning the Crystal Phase to Form MnGaOx‐Spinel for Highly Efficient Syngas to Light Olefins

“…= with a selectivity up to 80 % at 17 % CO conversion over ZnCrO x -SAPO-34, there is significant progress in both fundamental understanding and catalyst optimization. [3] To improve the activity, a wide range of metal oxides have been screened, including mono-metal oxides such as ZnO, [4] MnO, [5] In 2 O 3 , [6] Cr 2 O 3 , [7] bi-metal oxides with spinel crystal phase such as ZnCrO x , [3,8] ZnAlO x [9] and ZnGaO x , [10] solid solution such as ZnO-ZrO 2 , [11] MnO-Ga 2 O 3 , [12] ZnO-MnO, [13] Zr-doped Zn/ Al 2 O 3 , [14] Zr-doped In 2 O 3 , [15] MnCrO x , [16] CrMnGaO x , [17] and Zn x Ce 2À y Zr y O 4 . [18] Currently, most fundamental studies on OXZEO focus on Zn-based metal oxides, as they generally give higher activity than non-Zn-based oxides.…”

Rational Design of SAPO-34 Zeolite in Bifunctional Catalysts for Syngas Conversion into Light Olefins

“…Fischer–Tropsch synthesis (FTS) is a traditional strategy to convert syngas into hydrocarbons over Fe and Co catalysts; however, the Anderson–Schulz–Flory (ASF) model in FTS limits the selectivity of C 2–4 hydrocarbons (including olefins and paraffins), which is no more than 58%. , Recently, an elegant oxide–zeolite (OX-ZEO) route was proposed to selectively convert syngas into olefins (STO), liquid fuels and aromatics depending on the topologies of the zeolites, , which breaks the ASF distribution in FTS. A number of metal oxides, such as ZnCrO x , , Zn–ZrO 2 , , ZnAlO x ,, and MnGaO x , − and several kinds of zeolites, including SAPO-34, − SAPO-18, , AlPO-18, and SSZ-13, , have been intensively studied. In such an OX-ZEO catalyst system, the metal oxide is responsible for the syngas activation to generate intermediates like methanol and ketene, while the zeolite plays the role in tandem conversion of intermediates to target products .…”