Tag: manganese

Understanding the Role of Manganese in Fuel Production Catalysts

Understanding the Role of Manganese in Fuel Production Catalysts

SCIENTIFIC ACHIEVEMENT

Using specialized equipment at the Advanced Light Source (ALS), including a custom-built reaction cell, researchers uncovered the role of manganese in cobalt manganese oxide catalysts used for fuel production.

SIGNIFICANCE AND IMPACT

This work opens the door to improved catalyst designs that could decrease the production of harmful methane byproducts in a common petrochemical process. 

Sustainable fuel production

First developed in the 1920s, the Fischer-Tropsch synthesis remains a common chemical process used to convert carbon monoxide and hydrogen from coal into liquid hydrocarbons, or fuel. Cobalt is an efficient catalyst for this reaction, and its combination with manganese has been known for decades to further improve the process by promoting the preferential production of long-chain hydrocarbons over methane, a contributor to climate change. However, the molecular scale origin for why manganese improves the efficiency of this reaction remains unclear.

In this work, researchers uncovered the role of manganese in cobalt-manganese-oxide systems by combining well-defined model catalysts with advanced x-ray spectroscopy techniques. These results provide a platform for how customized equipment can answer challenging scientific questions and set the stage for new catalyst designs that may further decrease the production of methane during Fischer-Tropsch synthesis.

Custom-built instrumentation

Numerous studies have investigated the mechanisms for catalytic performance in cobalt-manganese-oxide systems, proposing particular interfaces, mixed oxides, or nanostructures as reasons for the improved efficiency. However, due to the heterogeneity of widely used powder catalysts, resulting in separated domains of cobalt and manganese, the molecular-scale mechanism of these catalysts remains under debate. To circumvent this, the researchers created model catalysts of well-defined cobalt-manganese-oxide nanocrystals and films where the components were intermixed at the sub-nanometer scale.

The model catalysts were investigated using ambient-pressure x-ray photoelectron spectroscopy (APXPS) at Beamline 9.3.2, which is equipped with commercial instrumentation uniquely designed for ambient-condition experiments that mimic real reaction conditions (this instrumentation was previously developed by the researchers, is now available at Beamline 9.0.2 and Beamline 11.0.2, and induced the application of APXPS at other synchrotron facilities). Similarly, to achieve realistic reaction conditions for x-ray absorption spectroscopy (XAS), a custom-built reaction cell was designed for Beamline 8.0.1, allowing experiments that typically occur under high vacuum to be performed under ambient pressure. The challenging and iterative process of perfecting this reaction cell was key to the success of this study, and the reaction cell is now available to other ALS users.

The magic of manganese

Using the custom-built reaction cell for XAS, the researchers were able to observe the real-time breakdown of carbon monoxide during the introduction of hydrogen to the cobalt-manganese-oxide catalyst at ambient conditions. Next, APXPS showed a significant increase in CHx hydrocarbon species after the addition of carbon monoxide and hydrogen on the cobalt-manganese-oxide catalyst surface–which was in stark contrast to the systems without manganese, where the production of cobalt carbide was more dominant instead. In other words, these results demonstrated that the addition of manganese creates more CHx, which ultimately allows for the production of more long-chain hydrocarbons.

The ALS data was complemented by computational density functional theory (DFT) calculations. DFT demonstrated that manganese helps with the production of long-chain hydrocarbons because manganese oxide binds with hydrogen, making it unavailable for reacting with CHx to stop propagation, resulting in less methane and more long-chain hydrocarbons. Moving forward, this work paves the way for improved catalyst designs that can make these reactions even more efficient.

Read more on ALS website

Possible green solution for manganese-contaminated soils

Possible green solution for manganese-contaminated soils

Manganese (Mn) is an essential micronutrient for plants, but at high concentrations, it can become toxic. However, Eucalyptus tereticornis appears to be remarkably tolerant to Mn, even at levels well above those that would cause harm to other plant species. The mechanism(s) underlying this ability were not understood based on scientific literature. From a study that monitored the Mn absorption in these plants, published in the Journal of Hazardous Materials, researchers from the Department of Plant Biology at the State University of Campinas (Unicamp) and from The Brazilian Synchrotron Light Laboratory (LNLS), from the Brazilian Center for Research in Energy and Materials (CNPEM), demonstrated how E. tereticornis can tolerate and detoxify high levels of Mn in its environment.  

The article, entitled “Tissue-level distribution and speciation of foliar manganese in Eucalyptus tereticornis by µ-SXRF and µ-XANES shed light on its detoxification mechanisms” led by Vinicius H. De Oliveira at Unicamp, presents the locations in the plant organism where Mn is accumulated, in what forms this element is assimilated, and even elucidates some of the mechanisms responsible for this ability to tolerate high concentrations of the metal used by E. tereticornis. This characteristic could be explored for environmental remediation purposes, particularly in contaminated soils.  

According to LNLS Soil Science Advisor, Dr. Dean Hesterberg, one of the article’s authors, it is not just the total Mn concentration that is important for understanding contaminated soils. “In acidic soils and especially under reducing redox conditions, manganese minerals are more soluble, which generally increases Mn availability for plant uptake. This can impact plants, which mainly absorb dissolved Mn. And, in Brazil, there are many acidic soils”, says Hesterberg.  

Synchrotron radiation imaging techniques

To gain evidence of how eucalyptus tolerates Mn-rich soils, researchers mapped the Mn distribution within Eucalyptus tereticornis leaves over time. This was possible through advanced techniques available at the Carnaúba beamline of the electron accelerator and synchrotron light generator, Sirius. The techniques used in the work included synchrotron micro scanning X-ray fluorescence imaging (µ-SXRF) and micro X-ray Absorption Near-Edge Structure (µ-XANES) spectroscopy.

Both use synchrotron radiation, a type of light released when electrons are accelerated to speeds very close to that of light. This usually happens by making them travel in a circular path, through strong magnetic fields, as is the case with the Sirius machine. Synchrotron light is incredibly bright and tunable over a wide range of wavelengths. In this way, the Carnaúba beamline uses light at X-ray wavelengths produced by the Sirius accelerator.

µ-SXRF

The synchrotron micro scanning X-ray fluorescence imaging (µ-SXRF) technique is used to investigate the elemental distribution and composition of materials on a microscopic scale. Fluorescence occurs because when materials are exposed to X-rays, atoms in the sample are excited and emit secondary (or fluorescent) X-rays when de-excited. The energy of these emissions serves as a fingerprint of each chemical element. This allows scientists to identify and quantify the composition of the studied material.  

LNLS/CNPEM researcher Dr. Carlos Alberto Pérez, one of the study’s authors, explains a little about how the technique works. “The µ-SXRF works based on X-ray optical equipment. The equipment has a monochromator, a crystal that defines a specific energy for the sample excitation. Another part of the equipment is the nanofocusing of this monochromatic light. This way, an X-ray beam that is about 100 times smaller than a human hair is created”.  

Through this beam of light, researchers are able to scan the sample, point by point, which generates an image with thousands of pixels. X-ray fluorescence is emitted as the beam hits each of these points. At the end, the pixels are computed using a program to generate an image, called elemental map. 

Elemental maps can be constructed for several specific chemical elements. In the case of the research published in the Journal of Hazardous Materials, the group of scientists assembled the elemental map of Mn in eucalyptus tissues. Thus, they were able to compare the presence of Mn in the plant’s leaf tissues, when it grew with an abundance of Mn and when it grew with normal amounts of the metal.  

μ-XANES

Micro-X-Ray Absorption Near Edge Structure (μ-XANES) spectroscopy, in turn, is used to probe the chemical state and electronic structure of specific elements in a sample. It is a sub-technique of X-ray Absorption Spectroscopy (analysis of how a sample absorbs X-rays), focusing on the energy band near the absorption edge of the element being studied. That is why the technique’s name brings the term ‘near the edge’.  

Hesterberg says that “unlike µ-SXRF, which is a fixed energy and scanning technique, µ-XANES is a variable energy technique. The absorption edge region is where there is a large increase in X-ray absorption by the sample”.  

Analysis of the edge region made it possible to discover the manganese oxidation state, that is, whether the element was in the form Mn²⁺, Mn³⁺ or Mn⁴⁺. Therefore, the technique allowed the researchers to understand if the manganese was in an oxidized form, or in a mineral state, and what coordinating atoms are likely around it. This means understanding what strategies eucalyptus uses to detoxify itself from the metal.  

Read more on CNPEM website

Image: Detectors around a sample being measured at the Sirius’ Carnaúba beamline.

Manganese Cathodes Could Boost Lithium-ion Batteries

Manganese Cathodes Could Boost Lithium-ion Batteries

Rechargeable lithium-ion batteries are growing in adoption, used in devices like smartphones and laptops, electric vehicles, and energy storage systems. But supplies of nickel and cobalt commonly used in the cathodes of these batteries are limited. New research led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) opens up a potential low-cost, safe alternative in manganese, the fifth most abundant metal in the Earth’s crust.

Researchers showed that manganese can be effectively used in emerging cathode materials called disordered rock salts, or DRX. Previous research suggested that to perform well, DRX materials had to be ground down to nanosized particles in an energy-intensive process. But the new study found that manganese-based cathodes can actually excel with particles that are about 1000 times larger than expected. The work was published Sept. 19 in the journal Nature Nanotechnology.

“There are many ways to generate power with renewable energy, but the importance lies in how you store it,” said Han-Ming Hau, who researches battery technology as part of Berkeley Lab’s Ceder Group and is a PhD student at UC Berkeley. “By applying our new approach, we can use a material that is both earth-abundant and low-cost, and that takes less energy and time to produce than some commercialized Li-ion battery cathode materials. And it can store as much energy and work just as well.”

The researchers used a novel two-day process that first removes lithium ions from the cathode material and then heats it at low temperatures (about 200 degrees Celsius). This contrasts with the existing process for manganese-based DRX materials, which takes more than three weeks of treatment.

Researchers used state-of-the-art electron microscopes to capture atomic-scale pictures of the manganese-based material in action. They found that after applying their process, the material formed a nanoscale semi-ordered structure that actually enhanced the battery performance, allowing it to densely store and deliver energy.

The team also used different techniques with X-rays to study how battery cycling causes chemical changes to manganese and oxygen at the macroscopic level. By studying how the manganese material behaves at different scales, the team opens up different methods for making manganese-based cathodes and insights into nano-engineering future battery materials.

Read more on ALS website

Image: A new process for manganese-based battery materials lets researchers use larger particles, imaged here by a scanning electron microscope. 

Credit: Han-Ming Hau/Berkeley Lab and UC Berkeley

Sodium-ion batteries: How doping works

Sodium-ion batteries: How doping works

Sodium-ion batteries still have a number of weaknesses that could be remedied by optimising the battery materials. One possibility is to dope the cathode material with foreign elements. A team from HZB and Humboldt-Universität zu Berlin has now investigated the effects of doping with Scandium and Magnesium. The scientists collected data at the X-ray sources BESSY II, PETRA III, and SOLARIS to get a complete picture and uncovered two competing mechanisms that determine the stability of the cathodes.

Lithium-ion batteries (LIB) have the highest possible energy density per kilogramme, but lithium resources are limited. Sodium, on the other hand, has a virtually unlimited supply and is the second-best option in terms of energy density. Sodium-ion batteries (SIBs) would therefore be a good alternative, especially if the weight of the batteries is not a major concern, for example in stationary energy storage systems.

However, experts are convinced that the capacity of these batteries could be significantly increased by a targeted material design of the cathodes. Cathode materials made of layered transition metal oxides with the elements nickel and manganese (NMO cathodes) are particularly promising. They form host structures in which the sodium ions are stored during discharge and released again during charging. However, there is a risk of chemical reactions which may initially improve the capacity, but ultimately degrade the cathode material through local structural changes. This has the consequence of reducing the lifetime of the sodium-ion batteries.

“But we need high capacity with high stability,” says Dr Katherine Mazzio, who is a member of the joint research group Operando Battery Analysis at HZB and the Humboldt-Universität zu Berlin, headed by Prof Philipp Adelhelm. Spearheaded by PhD student Yongchun Li, they have now investigated how doping with foreign elements affects the NMO cathodes. Different elements were selected as dopants that have similar ionic radii to nickel (Ni 2+), but different valence states: magnesium (Mg 2+) ions or scandium ions (Sc 3+). 

Read more on HZB website

Image: The schematic illustration shows a sodium ion battery: The positive electrode or cathode (left) consists of layered transition metal oxides which form a host structure for sodium ions. The transition metal nickel can be replaced either by magnesium or scandium ions. 

Credit: HZB