Hogalat: A CO catalyst used in filter respirators at room temperature

I. Introduction

In accidents such as building fires and coal mine gas explosions, carbon monoxide (CO) is the main toxic gas causing casualties. CO is colorless and odorless, and its binding capacity to hemoglobin is approximately 240 to 250 times that of oxygen. Exposure to 0.1% CO in the air by volume for about 30 minutes can cause unconsciousness or even death.

Personal protective equipment against CO is divided into two categories: self-contained (e.g., compressed oxygen respirators) and filtering equipment. Filtering equipment is small, lightweight, and requires no external air source, making it the primary choice for escape scenarios. The effectiveness of this type of equipment in eliminating CO depends on its core functional material—Hopcalite.

II. Material Definition and Chemical Composition

Hopcalite is a non-precious metal catalyst composed of active manganese dioxide (MnO₂) and copper oxide (CuO). The classic binary formulation has a mass ratio of MnO₂:CuO = 3:2 or 2:3. After co-precipitation or mechanical mixing, it is calcined at high temperature to form granules or flakes. To improve moisture resistance or thermal stability, quaternary formulations with added cobalt oxide (Co₃O₄) or a small amount of silver (Ag) are also used industrially.

III. Mechanism of Action: Catalytic Oxidation at Room Temperature

The elimination mechanism of CO by horgalat agents is **heterogeneous catalytic oxidation**, rather than adsorption or physical interception. The overall reaction is as follows:

2CO + O₂ → (horgalat agent, room temperature) → 2CO₂

Under catalyst-free conditions, this reaction requires temperatures above 200℃ to proceed significantly. Horgalat agents, through electron migration between surface Mn⁴⁺/Mn³⁺ and Cu²⁺ and the participation of lattice oxygen, significantly reduce the activation energy, enabling CO to be rapidly converted to CO₂ within a temperature range of **-20℃ to 50℃**.

The catalytic process consists of three steps: CO adsorbs onto the active sites on the catalyst surface; adsorbed CO reacts with lattice oxygen to generate CO₂ and then desorbs; gaseous O₂ fills the oxygen vacancies, restoring catalyst activity. Hogalat is theoretically not consumed in the reaction; performance degradation mainly stems from water vapor poisoning, dust accumulation, or thermal sintering.

IV. Integration Methods in Filter-Type Respirators

Hogalat is currently mainly used in two types of filter-type respiratory protective equipment: fire-fighting filter-type self-rescue respirators (suitable for escape from building fire scenes, with a standard protection time of 15 to 30 minutes, according to GB 21976.7) and mining filter-type self-rescue devices (suitable for evacuation after underground explosions or fires, with a standard protection time of not less than 30 minutes, according to GB 8159).

In the above equipment, hogalat is filled into the filter canister or cartridge in the form of granules or cylindrical molded bodies. A complete gas filter canister is not simply filled with catalyst; it employs a multi-layered, series-connected structure with four functional layers arranged sequentially from the inlet to the outlet.

The first layer is the smoke filter layer, composed of ultra-fine fiber material, used to intercept solid particles and soot in the flue gas. This layer prevents particles from entering subsequent catalyst layers and causing physical blockage, thus ensuring smooth airflow and extending the effective lifespan of the catalyst.

The second layer is the desiccant layer, typically filled with silica gel or molecular sieves. Because hornolatrix is extremely sensitive to humidity—when the relative humidity exceeds 50%, water molecules compete with CO for active sites on the catalyst surface, leading to a sharp drop in catalytic efficiency and even irreversible deactivation—the gas must be dried before contacting the hornolatrix to control the relative humidity below 50%.

The third layer is the hornolatrix layer, the core functional unit of the entire filter canister. This layer is filled with shaped hornolatrix particles with a particle size of 2 to 4 millimeters, responsible for the catalytic conversion of highly toxic CO into harmless CO₂. As gas passes through this layer, CO is rapidly oxidized on the catalyst surface, and the CO concentration in the outlet gas can drop below safe limits within seconds.

The fourth layer is a heat dissipation or buffer layer, composed of a metal mesh or inert ceramic particles. The CO catalytic oxidation reaction is exothermic; in high CO concentration environments, the heat of reaction can cause the outlet gas temperature to rise. The heat dissipation layer absorbs some of the heat generated by the reaction, lowering the temperature of the air entering the wearer's respiratory tract and improving comfort and safety.

These four layers are arranged in series within the filter canister. Gas passes sequentially through the smoke filter layer, desiccant layer, horgalactone layer, and heat dissipation layer, ultimately becoming clean air for the wearer to inhale. This design achieves an engineering balance between CO conversion efficiency, breathing resistance, and safety.

V. Performance Advantages and Technical Limitations

Advantages: High efficiency at room temperature, no preheating or external energy required; CO processing capacity per unit volume is superior to adsorption materials; using manganese and copper as raw materials, the cost is significantly lower than precious metal catalysts such as platinum and palladium.

Main limitations: When relative humidity exceeds 50%, water molecules compete with CO for active sites, leading to a sharp decrease in conversion efficiency and potentially irreversible deactivation; when the inlet CO concentration is too high (exceeding 2.5% by volume), the exothermic reaction can cause the bed temperature to exceed 600℃, triggering catalyst sintering and failure; once poisoned by water vapor or particulate matter, performance cannot be restored under on-site conditions.

Therefore, hogalat is suitable for short-term, low-humidity, medium-concentration CO emergency protection scenarios, but not for high-humidity, high-concentration, or ultra-long-term continuous operations.

VI. Engineering Significance and Selection Basis

Under current technological conditions, hogalat is the only core material for filter-type respirators that has undergone large-scale industrial verification and can efficiently eliminate CO at room temperature through catalytic oxidation. Its 15 to 30 minutes of effective protection time, supported by accident statistics, is sufficient to support personnel evacuation in the early stages of a fire or mine disaster.

It should be particularly noted that while both hogalat and activated carbon appear as dark granules, their functions are completely different. Activated carbon, based on a physical adsorption mechanism, is effective against large molecular gases such as benzene compounds, chlorine, and organic vapors, but has virtually no adsorption capacity for carbon monoxide. A qualified filter canister must, within its rated protection time, ensure that the CO concentration after purification meets national standards (GB 21976.7 specifies a CO concentration not exceeding 200 ppm). Procurement and selection should be based on products with CCC mandatory certification and valid type test reports.

VII. Conclusion

Hogaratte, as a functional catalytic material, is valuable in the field of filter-based personal protective equipment due to its ability to "chemically convert" carbon monoxide—transforming toxic gases into harmless components through surface catalytic reactions. Understanding its material properties, mechanism of action, and application limitations is a fundamental prerequisite for ensuring the true effectiveness of personal protective equipment.

Author: Gloria
Date: 2026-04-29