Cr³⁺–Co_0.054Ni_0.018Mg_0.93O Solid-Solution Catalysts for High-Pressure Syngas Production: Effect of Chromium on the Reduction and Catalysis

Abstract

Adding Cr to heat-tolerant Co0.054Ni0.018Mg0.93O solid-solution catalysts for CH4/CO2/H2O reforming at 2.1 MPa allowed us to control the key properties determining the behavior of the supported catalysts, such as the reduction degree of the metal, metal particle size, and amount of exposed zerovalent metals. A small load of Cr [Cr/(Co + Ni) = 0.11 mol %] efficiently catalyzed Co2+ and Ni2+ reduction. This catalyst, which had abundant small alloy particles on the support material, resisted coking and oxidative deactivation, even under accelerated deterioration conditions. X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, extended X-ray absorption fine structure, and scanning transmission electron microscopy–energy-dispersive X-ray measurements indicated that Cr existed as a trivalent cation in a Cr x Co0.054Ni0.018Mg0.93O1+1.5x solid solution, leading to the formation of a divalent cation vacancy and that Cr3+ was abundant on the surface of the catalyst particles after calcination at 1373 K. The Cr3+ destabilized Co2+ and Ni2+ in the solid solution, especially on the surface of the catalyst particles and, thus, promoted Co2+ and Ni2+ reduction. However, excess Cr3+ induced sintering of the catalyst particles, resulting in aggregation of alloy particles and, thus, in an increased risk of coking.

Tuning the composition of metastable Co Ni Mg100−−(OH)(OCH3) nanoplates for optimizing robust methane dry reforming catalyst

“…In recent reports, combined strategies with reduced Ni particle size and addition of promoters have shown prominent coke-resistance performance in MDR [50][51][52]. Co-Ni alloy supported on MgO is a promising catalyst.…”

Sulfur-resistant and regenerable Ni/Co spinel-based catalysts for methane dry reforming

“…The faceting remains dominated by {111} faces with sharp angles between adjacent faces -often less than 120°providing a long length of well-ordered undercoordinated sites as well as well-ordered interfaces between the metal and oxide support. Nagaoka and coworkers 29,30 demonstrated that oxygen transfer at the metal-ZrO 2 interface is critical for oxidative sulfur removal in ZrO 2 -suppported Ni catalysts, but little is known about the effects of crystal orientation and local interfacial nanostructures on oxygen transfer. As discussed later, higher crystal perfection and faceting improve sulfur tolerance in the Ni-Co catalysts.…”

“…This mechanism parallels that of coking resistance in Ni/ZrO 2 , where Nagaoka and coworkers showed that the ZrO 2 support facilitates CO 2 activation and the resulting oxygen is exchanged at the metal/ZrO 2 interface to gasify adsorbed carbon species. 29,30 In the case of Ni/ZrO 2 , the variable valence of Zr and facile formation of oxygen vacancies are key to the presence of active oxygen species. For the spinel-supported catalyst of the form IJCo 0.375 Ni 0.375 Mg 0.25 )Al 2 O 4 , some Ni and Co remain in the remnant spinel after the reduction reaction at 900 °C and the remnant spinel is highly defective.…”