High Ammonia Uptake of a Metal–Organic Framework Adsorbent in a Wide Pressure Range

Abstract

Although numerous porous adsorbents have been investigated for NH3 capture applications, these materials often exhibit insufficient NH3 uptake, low NH3 affinity at the ppm level, and poor chemical stability against wet NH3 conditions. The NH3 capture properties of M2(dobpdc) complexes (M=Mg2+, Mn2+, Co2+, Ni2+, and Zn2+; dobpdc4−=4,4‐dioxidobiphenyl‐3,3‐dicarboxylate) that contain open metal sites is presented. The NH3 uptake of Mg2(dobpdc) at 298 K was 23.9 mmol g−1 at 1 bar and 8.25 mmol g−1 at 570 ppm, which are record high capacities at both pressures among existing porous adsorbents. The structural stability of Mg2(dobpdc) upon exposure to wet NH3 was superior to that of the other M2(dobpdc) and the frameworks tested. Overall, these results demonstrate that Mg2(dobpdc) is a recyclable compound that exhibits significant NH3 affinity and capacity, making it a promising candidate for real‐world NH3‐capture applications.

Constructing Well-Defined and Robust Th-MOF-Supported Single-Site Copper for Production and Storage of Ammonia from Electroreduction of Nitrate

“…As shown in Figure 5b, after humid NH 3 uptake, new peaks assigned to degenerated and symmetric deformations of Cu-NH 3 at 1625 cm −1 were detected, which demonstrates that NH 3 is coordinated to the open Cu metal sites. 14 On the basis of the above experimental and characterization results, the outstanding ability for production and storage of NH 3 from electroreduction of NO 3 − in Cu@Th-BPYDC is mainly ascribed to the following factors. First, the Cu species in Cu@Th-BPYDC presents unsaturated coordination, which is highly active for electrocatalysis.…”

“…This high uptake capacity is superior to those in most of the recently reported top-performing MOFs and porous polymers (Table S2). ,,− The significantly different NH 3 uptake capacities in Cu@Th-BPYDC and Cu-free Th-BPYDC strongly demonstrate that the open single-metal site Cu which serves as a Lewis acid site strongly interacts with NH 3 molecules to improve the NH 3 uptake capacity despite smaller BET surface areas in Cu@Th-BPYDC. Noticeably, the desorption isotherm of Cu@Th-BPYDC does not coincide with the adsorption curve (Figure a), indicating an irreversible interaction between Cu sites and NH 3 molecules without any treatment and the formation of chemisorption.…”

“… 10 − 13 In general, the adsorbent first must possess high stability owing to the strong corrosivity of NH 3 . 14 Second, the special functional groups, especially acidic sites, are generally necessary to strongly interact with basic NH 3 and achieve high total uptake and strong affinity. 15 − 17 However, at present, NH 3 production and storage were performed separately using different materials.…”

“…As shown in Figure 5 b, after humid NH 3 uptake, new peaks assigned to degenerated and symmetric deformations of Cu-NH 3 at 1625 cm –1 were detected, which demonstrates that NH 3 is coordinated to the open Cu metal sites. 14 …”

“…However, this is a high energy consumption manner. Thus, in recent years, different porous materials have been developed to store NH 3 due to its low energy consumption and convenient-to-operate manner. − In general, the adsorbent first must possess high stability owing to the strong corrosivity of NH 3 . Second, the special functional groups, especially acidic sites, are generally necessary to strongly interact with basic NH 3 and achieve high total uptake and strong affinity. − However, at present, NH 3 production and storage were performed separately using different materials.…”