Mn(I)-PNP pincer catalyzed sequential one-pot homogeneous CO 2 hydrogenation to CH 3 OH by molecular H 2 is demonstrated. The hydrogenation consists of two partsN-formylation of an amine utilizing CO 2 and H 2 , and subsequent formamide reduction to CH 3 OH, regenerating the amine in the process. A reported air-stable and welldefined Mn-PNP pincer complex was found active for the catalysis of both steps. CH 3 OH yields up to 84% and 71% (w.r.t amine) were obtained, when benzylamine and morpholine were used as amines, respectively; and a TON of up to 36 was observed. In our opinion, this study represents an important development in the nascent field of base-metal-catalyzed homogeneous CO 2 hydrogenation to CH 3 OH.

Amine-assisted homogeneous hydrogenation of CO2 to methanol is one of the most effective approaches to integrate CO2 capture with its subsequent conversion to CH3OH. The hydrogenation typically proceeds in two steps. In the first step the amine is formylated via an in situ formed alkylammonium formate salt (with consumption of 1 equiv of H2). In the second step the generated formamide is further hydrogenated with 2 more equiv of H2 to CH3OH while regenerating the amine. In the present study, we investigated the effect of molecular structure of the ruthenium pincer catalysts and the amines that are critical for a high methanol yield. Surprisingly, despite the high reactivity of several Ru pincer complexes [RuHClPNP R (CO)] (R = Ph/i-Pr/Cy/t-Bu) for both amine formylation and formamide hydrogenation, only catalyst Ru-Macho (R = Ph) provided a high methanol yield after both steps were performed simultaneously in one pot. Among various amines, only (di/poly)­amines were effective in assisting Ru-Macho for methanol formation. A catalyst deactivation pathway was identified, involving the formation of ruthenium biscarbonyl monohydride cationic complexes [RuHPNP R (CO)2]+, whose structures were unambiguously characterized and whose reactivities were studied. These reactivities were found to be ligand-dependent, and a trend could be established. With Ru-Macho, the biscarbonyl species could be converted back to the active species through CO dissociation under the reaction conditions. The Ru-Macho biscarbonyl complex was therefore able to catalyze the hydrogenation of in situ formed formamides to methanol. Complex Ru-Macho-BH was also highly effective for this conversion and remained active even after 10 days of continuous reaction, achieving a maximum turnover number (TON) of 9900.

The capture of CO 2 from concentrated emission sources as well as from air represents a process of paramount importance in view of the increasing CO 2 concentration in the atmosphere and its associated negative consequences on the biosphere. Once captured using various technologies, CO 2 is desorbed and compressed for either storage (carbon capture and storage (CCS)) or production of value-added products (carbon capture and utilization (CCU)). Among various products that can be synthesized from CO 2 , methanol and formic acid are of high interest because they can be used directly as fuels or to generate H 2 on demand at low temperatures (<100 °C), making them attractive hydrogen carriers (12.6 and 4.4 wt % H 2 in methanol and formic acid, respectively). Methanol is already produced in huge quantities worldwide (100 billion liters annually) and is also a raw material for many chemicals and products, including formaldehyde, dimethyl ether, light olefins, and gasoline. The production of methanol through chemical recycling of captured CO 2 is at the heart of the so-called "methanol economy" that we have proposed with the late Prof. George Olah at our Institute. Recently, there has been significant progress in the low-temperature synthesis of formic acid (or formate salts) and methanol from CO 2 and H 2 using homogeneous catalysts. Importantly, several studies have combined CO 2 capture and hydrogenation, where captured CO 2 (including from air) was directly utilized to produce formate and CH 3 OH without requiring energy intensive desorption and compression steps. This Account centers on that topic. A key feature in the combined CO 2 capture and conversion studies reported to date for the synthesis of formic acid and methanol is the use of an amine or alkali-metal hydroxide base for capturing CO 2 , which can assist the homogeneous catalysts in the hydrogenation step. We start this Account by examining the combined processes where CO 2 is captured in amine solutions and converted to alkylammonium formate salts. The effect of amine basicity on the reaction rate is discussed along with catalyst recycling schemes. Next, methanol synthesis by this combined process, with amines as capturing agents, is explored. We also examine the system developments for effective catalyst and amine recycling in this process. We next go through the effect of catalyst molecular structure on methanol production while elucidating the main deactivating pathway involving carbonylation of the metal center. The recent advances in first-row transition metal catalysts for this process are also mentioned. Subsequently, we discuss the capture of CO 2 using hydroxide bases and conversion to formate salts. The regeneration of the hydroxide base (NaOH or KOH) at low temperatures (80 °C) in cation-conducting direct formate fuel cells is presented. Finally, we review the challenges in the yet unreported integrated CO 2 capture by hydroxide bases and conversion to methanol process.

Top-gated, few-layer graphene field-effect transistors (FETs) fabricated on thermally decomposed semi-insulating 4H-SiC substrates are demonstrated. Physical vapor deposited SiO2 is used as the gate dielectric. A two-dimensional hexagonal arrangement of carbon atoms with the correct lattice vectors, observed by high-resolution scanning tunneling microscopy, confirms the formation of multiple graphene layers on top of the SiC substrates. The observation of n-type and p-type transition further verifies Dirac Fermions’ unique transport properties in graphene layers. The measured electron and hole mobilities on these fabricated graphene FETs are as high as 5400 and 4400cm2∕Vs, respectively, which are much larger than the corresponding values from conventional SiC or silicon.

Herein we report an efficient and recyclable system for tandem CO capture and hydrogenation to methanol. After capture in an aqueous amine solution, CO is hydrogenated in high yield to CHOH (>90%) in a biphasic 2-MTHF/water system, which also allows for easy separation and recycling of the amine and catalyst for multiple reaction cycles. Between cycles, the produced methanol can be conveniently removed in vacuo. Employing this strategy, catalyst Ru-MACHO-BH and polyamine PEHA were recycled three times with 87% of the methanol producibility of the first cycle retained, along with 95% of catalyst activity after four cycles. CO from dilute sources such as air can also be converted to CHOH using this route. We postulate that the CO capture and hydrogenation to methanol system presented here could be an important step toward the implementation of the carbon neutral methanol economy concept.