High CO Methanation Performance of Two-Dimensional Ni/MgAl Layered Double Oxide with Enhanced Oxygen Vacancies via Flash Nanoprecipitation

Abstract

As a methanation tool, two-dimensional (2D) carrier-loaded Ni has attracted the attention of many researchers. We successfully prepared 2D MgAl layered double oxides (LDO) carriers via flash nanoprecipitation (FNP). Compared to the LDO samples prepared by conventional co-precipitation (CP), the 2D MgAl-LDO (FNP) has more oxygen vacancies and more exposed active sites. The Ni/MgAl-LDO (FNP) catalyst demonstrates a CO conversion of 97%, a CH 4 selectivity of 79.8%, a turnover frequency of 0.141 s −1 , and a CH 4 yield of 77.4% at 350 • C. The weight hourly space velocity was 20,000 mL·g −1 ·h −1 with a synthesis gas flow rate of 65 mL·min −1 , and a pressure of 1 atm. A control experiment used the CP method to prepare Ni/MgAl-LDO. This material exhibits a CO conversion of 81.1%, a CH 4 selectively of 75.1%, a TOF of 0.118 s −1 , and a CH 4 yield of 61% at 450 • C. We think that this FNP method can be used for the preparation of more 2D LDO catalysts. molecular sieve catalysts (Ni/3D-MCM-41), the Ni/2D-SiO 2 catalyst showed remarkable catalytic activity with high CO conversion and CH 4 selectivity at 450 • C.Natural mineral vermiculite (VMT) with a 2D structure as a catalyst support was reported [12]. Li et al. [13] attempted to expand multilayered vermiculite as a catalyst support and successfully synthesized NiO/VMT composite by microwave irradiation-assisted synthesis (MIAS). The Ni/VMT (MIAS) resulted in highly dispersed active sites and exhibited excellent catalysis performance, including a 99.6% CO conversion and 93.8% CH 4 selectivity at 400 • C. Zhang et al. [14] synthesized a 2D plasma-treated vermiculite (PVMT) with low Ni loading (0.5 wt %) via a plasma irradiation method (PIM). The PIM-Ni/PVMT exhibited superior catalytic performance, and the plasma-treated catalyst PIM-Ni/PVMT achieved a CO conversion of 93.5% and a turnover frequency (TOF) of 0.8537 s −1 at a temperature of 450 • C and a pressure of 1.5 MPa.Other 2D catalysts for CO methanation include 2D Ni-based layered double oxides (LDO) from layered double hydroxides (LDH). These systems are popular because of their high Ni dispersibility [15,16]. NiAl-LDO offers excellent activity for methanation under 2.0 MPa and 527 • C. NiAl-LDO catalysts with 56.5 wt % Ni achieved 97% CO conversion in a pilot methanation unit. Bian et al.[17] synthesized a NiAl-LDO catalyst that displayed high catalytic stability due to high Ni dispersion and strong resistance to coke deposition versus the impregnated catalyst. Nearly 100% CO conversion was achieved with reaction temperatures between 400 and 500 • C with a weight hourly space velocity (WHSV) of 300,000 mL·g −1 ·h −1 .Mg adulteration can also improve the anti-coke ability of Ni-based catalysts. Li et al.[18] synthesized Ni-Mg-Al LDO (i.e., NiMg8, Ni/Mg = 1/8) via a co-precipitation method. The as-obtained catalyst with 11 wt % Ni had the best CO methanation performance due to the small size of Ni particles and high Ni dispersion. The NiMg8 had excellent performance: 99.8% CO conversion and 73.6% CH 4 selectivi...

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