An efficient and direct method of catalytic conversion of methane to liquid methanol and other oxygenates would be of considerable practical value. However, it remains an unsolved problem in catalysis, as typically it involves expensive or corrosive oxidants or reaction media that are not amenable to commercialization. Although methane can be directly converted to methanol using molecular oxygen under mild conditions in the gas phase, the process is either stoichiometric (and therefore requires a water extraction step) or is too slow and low-yielding to be practical. Methane could, in principle, also be transformed through direct oxidative carbonylation to acetic acid, which is commercially obtained through methane steam reforming, methanol synthesis, and subsequent methanol carbonylation on homogeneous catalysts. However, an effective catalyst for the direct carbonylation of methane to acetic acid, which might enable the economical small-scale utilization of natural gas that is currently flared or stranded, has not yet been reported. Here we show that mononuclear rhodium species, anchored on a zeolite or titanium dioxide support suspended in aqueous solution, catalyse the direct conversion of methane to methanol and acetic acid, using oxygen and carbon monoxide under mild conditions. We find that the two products form through independent pathways, which allows us to tune the conversion: three-hour-long batch-reactor tests conducted at 150 degrees Celsius, using either the zeolite-supported or the titanium-dioxide-supported catalyst, yield around 22,000 micromoles of acetic acid per gram of catalyst, or around 230 micromoles of methanol per gram of catalyst, respectively, with selectivities of 60-100 per cent. We anticipate that these unusually high activities, despite still being too low for commercial application, may guide the development of optimized catalysts and practical processes for the direct conversion of methane to methanol, acetic acid and other useful chemicals.

Mild oxidation of methane to methanol or acetic acid on supported isolated rhodium catalysts

Carbon monoxide (CO) produced in many large-scale industrial oxidation processes is difficult to separate from nitrogen (N2), and afterward, CO is further oxidized to carbon dioxide. Here, we report a soft nanoporous crystalline material that selectively adsorbs CO with adaptable pores, and we present crystallographic evidence that CO molecules can coordinate with copper(II) ions. The unprecedented high selectivity was achieved by the synergetic effect of the local interaction between CO and accessible metal sites and a global transformation of the framework. This transformable crystalline material realized the separation of CO from mixtures with N2, a gas that is the most competitive to CO. The dynamic and efficient molecular trapping and releasing system is reminiscent of sophisticated biological systems such as heme proteins.

https://science.sciencemag.org/content/sci/343/6167/167.full.pdf

Self-Accelerating CO Sorption in a Soft Nanoporous Crystal

Novel acetic acid processes and catalysts have been introduced, commercialized, and improved continuously since the 1950s. The objective of the development of new acetic acid processes has been to reduce raw material consumption, energy requirements, and investment costs. At present, industrial processes for the production of acetic acid are dominated by methanol carbonylation and the oxidation of hydrocarbons such as acetaldehyde, ethylene, n-butane, and naphtha. This paper discusses advances in acetic acid processes and catalysts according to the following routes: (1) methanol carbonylation; (2) methyl formate isomerization; (3) synthesis gas to acetic acid; (4) vapor phase oxidation of ethylene, and (5) other novel technologies.

Recent advances in processes and catalysts for the production of acetic acid

Recent advances in the methanol carbonylation reaction into acetic acid

Long-chain alcohols synthesis (LAS, C5+OH) from syngas provides a promising route for the conversion of coal/biomass/natural gas into high-value chemicals. Cu-Fe binary catalysts, with the merits of cost effectiveness and high CO conversion, have attracted considerable attention. Here we report a nano-construct of a Fe5C2-Cu interfacial catalyst derived from Cu4Fe1Mg4-layered double hydroxide (Cu4Fe1Mg4-LDH) precursor, i.e., Fe5C2 clusters (~2 nm) are immobilized onto the surface of Cu nanoparticles (~25 nm). The interfacial catalyst exhibits a CO conversion of 53.2%, a selectivity of 14.8 mol% and a space time yield of 0.101 g gcat−1 h−1 for long-chain alcohols, with a surprisingly benign reaction pressure of 1 MPa. This catalytic performance, to the best of our knowledge, is comparable to the optimal level of Cu-Fe catalysts operated at much higher pressure (normally above 3 MPa). Long-chain alcohols synthesis from syngas conversion is a promising route for the production of high-value chemicals. Here the authors show that a heterogeneous Fe5C2/Cu catalyst derived from layered double hydroxides precursor exhibits excellent performance with a space time yield of 0.101 g gcat−1 h−1 at a low pressure of 1 MPa.

/pdf/interfacial-fe-5-c-2-cu-catalysts-toward-low-pressure-syngas-499v5l2akb.pdf

F. E. Paulik

Papers

Novel catalysts for the low-pressure carbonylation of methanol to acetic acid