Hydrogenated Borophene Shows Catalytic Activity as Solid Acid

Abstract

Hydrogen boride (HB) or hydrogenated borophene sheets are recently realized two-dimensional materials that are composed of only two light elements, boron and hydrogen. However, their catalytic activity has not been experimentally analyzed. Herein, we report the catalytic activity of HB sheets in ethanol reforming. HB sheets catalyze the conversion of ethanol to ethylene and water above 493 K with high selectivity, independent of the contact time, and with an apparent activation energy of 102.8 ± 5.5 kJ/mol. Hence, we identify that HB sheets act as solid-acid catalysts.

Ethanol–ethylene conversion mechanism on hydrogen boride sheets probed by in situ infrared absorption spectroscopy

“…21 Our recent study revealed that HB sheets in their hydrogen-deficient state (H : B ratio of approximately 1 : 2.5 AE 0.5) catalyze the conversion of ethanol to ethylene and water above 493 K with high selectivity independent of the contact time, and an apparent activation energy of 102.8 AE 5.5 kJ mol À1 . 22 The activation energy of this process is comparable to those reported for the catalytic dehydration of ethanol over Al 2 O 3 (53-155 kJ mol À1 ), 23,24 the Lewis acidic catalyst Zr-KIT-6 (79 kJ mol À1 ), 25 silica-alumina (125.5 kJ mol À1 ), 26 and the microporous Fe-ZSM-5 (137.7-271.1 kJ mol À1 ). 27 The formation rate of ethylene on the HB catalyst is lower than that offered by state-of-the-art catalysts, but is of the same order as that on the commercial SynDol (Al 2 O 3 -MgO/SiO 2 ) catalyst.…”

“…HB sheets were prepared using a previously reported ionexchange method. [17][18][19][20][21][22] More specifically, MgB 2 powder (1.0 g, 99%, Rare Metallic Co., Ltd, Tokyo, Japan) in acetonitrile (300 mL, 99.5%, Wako Pure Chemical Industries Ltd, Osaka, Japan) was added to a mixture of an ion-exchange resin (60 mL, Amberlite IR120B hydrogen, Organo Corp., Tokyo, Japan) and acetonitrile (200 mL) in a Schlenk flask under a nitrogen atmosphere. Water was carefully removed due to the facile hydrolysis of MgB 2 .…”

“…S1, ESI †). [17][18][19][20][21][22] For in situ FT-IR spectroscopy analysis, we used a homemade vacuum system (Fig. S2, ESI †) coupled with an FT-IR spectrometer (FT/IR-610, Jasco, Ltd, Tokyo, Japan) to observe the structural changes in the HB sheets during heating under vacuum (1.0 Â 10 À6 Torr) after exposure to ethanol vapor (B44 Torr in 123 cc) for 1 h at room temperature (B300 K).…”

“…27 The formation rate of ethylene on the HB catalyst is lower than that offered by state-of-the-art catalysts, but is of the same order as that on the commercial SynDol (Al 2 O 3 -MgO/SiO 2 ) catalyst. 22 Therefore, HB sheets can be regarded as a solid-acid catalyst. However, the mechanism of HB catalysis has not yet been elucidated, and the active sites have not been identified.…”

Diborane Concatenation Leads to New Planar Boron Chemistry

“…Moreover, connections between the polyhedral boranes and the metal borides can be drawn [13] . Notably, recent works have shown that extraction of a single hexagonal layer of boron atoms from superconducting MgB 2 is possible in the form of 2‐D borane layers (BH) 1 , [14–18] known as borophane, hydrogen boride or hydrogenated borophene. This 2D (BH) 1 hexagonal structure is very similar to graphene [19] with two exceptions, apart from the atom nature: (i) there are two different B–B distances for each hexagon, short d (BB) and long d (BB) b and (ii) there are two bridge hydrogen atoms (H b ), one above and one below the xy plane in the mid‐point of every alternating long (BB) b bond, as shown in Figure 1b.…”