Grafting Ni particles onto SBA-15, and their enhanced performance for CO₂ methanation

Abstract

By a post synthesis method, nickel (Ni) particles could be grafted onto SBA-15 for the first time through a chemical bond (-O-Ni-O-Si-O-) formation between silicon (Si) and Ni via oxygen (O) using Ni ammonia (NH3) complex ions (Ni(NH3)x) 2+ with NH3/Ni mole ratio of 1~5, which existed as Ni phyllosilicate on SBA-15 surface, while Ni particles could not be grafted onto SBA-15 in the absence of NH4OH (NH3/Ni mole ratio of 0). NH3/Ni mole ratio of 2~4 was suitable grafting conditions, which could give a product with the closest Ni amount to raw. This product obtained was named Ni-grafted SBA-15 sample. XPS, UV-vis and H2-TPR analyses demonstrated that a chemical bond was formed between Ni and silicon (Si) via oxygen (O), and no bulk nickel oxides existed in Ni-grafted SBA-15 sample. The formation of -O-Ni-O-Si-O-was completed via the reaction between hydrolyzate Ni(OH)(NH3)x-1) + from (Ni(NH3)x) 2+ and ≡Si-OH (silanol sites) on SBA-15 surface. Ni-grafted SBA-15 catalyst suited CO2 methanation, resulting in higher CO2 conversion and methane selectivity than NiO dispersed SBA-15 catalyst obtained by conventional post synthesis method. The activation energy for CO2 methanation increased with decreasing initial Ni amount used. The rate equation for CO2 methanation could be expressed as: r = kCCO 2 0.64 CH 2 4.05 , C was concentration. Ni-grafted SBA-15 catalyst had high thermal stability for CO2 methanation.

Micro- and mesoporous supports for CO2 methanation catalysts: A comparison between SBA-15, MCM-41 and USY zeolite

“…On the contrary, the peaks attributed to the MCM-41 structure (~ 2.1, 4.0 and 4.6º 24 ) were not clearly observed for the Ni and Ni-Ce/MCM-41 catalysts, which could be due to a migration of a greater fraction of metallic species to the pores during the catalytic test and/or a partial loss of the ordered hexagonal pore structure arrangement of the material 13,25 . Regarding the wide angle patterns, all samples presented an important decrease on the peaks intensity as already seen in the literature 26 , being only observed in some cases the characteristic peaks of Ni 0 . …”

Identification of Outer and Inner Nickel Particles in a Mesoporous Support: How the Channels Modify the Reducibility of Ni/SBA‐15 Catalysts

“…[7,9,10] On the other hand, the Ni/SBA-15-DPs ample is dominated by am ain peak centereda th igh temperature (660 8C), accompanied by as mall and wide shoulder between 350 and 450 8C, once again approximately corresponding to thet emperature reduction interval of massive NiO, whose TPR profile is also included in Figure 2. It is well-known [11,12] that during the DP preparation procedure the silicas urfaceo fSBA-15 is partially dissolved, leadingt ot he formation of as urface nickel silicate phase which, as previously reported, reducesa tt his hight emperature.After ar eductiont reatment with hydrogen at 750 8C, XRD (Supporting Information, Figure S1) showsi nb oth systems the formationo fam etallic nickel phase but with differentc rystallite sizes. The TEM image of the reduced DP catalyst (Fig-ure 1d)s hows well and homogeneously dispersed nickel particles, with am ean diameter of about 4.5 nm.…”

“…On the other hand, the Ni/SBA‐15‐DP sample is dominated by a main peak centered at high temperature (660 °C), accompanied by a small and wide shoulder between 350 and 450 °C, once again approximately corresponding to the temperature reduction interval of massive NiO, whose TPR profile is also included in Figure . It is well‐known that during the DP preparation procedure the silica surface of SBA‐15 is partially dissolved, leading to the formation of a surface nickel silicate phase which, as previously reported, reduces at this high temperature.…”

Synthesis of new TCH/Ni‐based nanocomposite supported on SBA‐15 and its catalytic application for preparation of benzimidazole and perimidine derivatives

“…Generally, highly dispersed Ni‐SBA‐15 can be prepared by direct synthesis method and post‐synthesis procedures, but it is difficult to obtain strongly interacting Ni ions with ordered mesoporous silica support . Therefore, developing a new and efficient route for stable grafting of Ni ion onto SBA‐15 surface remains an interesting and important topic especially in catalytic organic transformations.…”